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• Do’s and Don’ts Building SharePoint Applications

  - by Bil Simser

  SharePoint is a great platform for building quick LOB applications. Simple things from employee time trackers to server and software inventory to full blown Help Desks can be crafted up using SharePoint from just customizing Lists. No programming necessary. However there are a few tricks I’ve painfully learned over the years that you can use for your own solutions. DO What’s In A Name? When you create a new list, column, or view you’ll commonly name it something like “Expense Reports”. However this has the ugly effect of creating a url to the list as “Expense%20Reports”. Or worse, an internal field name of “Expense_x0x0020_Reports” which is not only cryptic but hard to remember when you’re trying to find the column by internal name. While “Expense Reports 2011” is user friendly, “ExpenseReports2011” is not (unless you’re a programmer). So that’s not the solution. Well, not entirely. Instead when you create your column or list or view use the scrunched up name (I can’t think of the technical term for it right now) of “ExpenseReports2011”, “WomenAtTheOfficeThatAreMen” or “KoalaMeatIsGoodWhenBroiled”. After you’ve created it, go back and change the name to the more friendly “Silly Expense Reports That Nobody Reads”. The original internal name will be the url and code friendly one without spaces while the one used on data entry forms and view headers will be the human version. Smart Columns When building a view include columns that make sense. By default when you add a column the “Add to default view” is checked. Resist the urge to be lazy and leave it checked. Uncheck that puppy and decide consciously what columns should be included in the view. Pick columns that make sense to what the user is trying to do. This means you have to talk to the user. Yes, I know. That can be trying at times and even painful. Go ahead, talk to them. You might learn something. Find out what’s important to them and why. If they’re doing something repetitively as part of their job, try to make their life easier by including what’s most important to them. Do they really need to see the Created *and* Modified date of a document or do they just need the title and author? You’ll only find out after talking to them (or getting them drunk in a bar and leaving them in the back alley handcuffed to a garbage bin, don’t ask). Gotta Keep it Separated Hey, views are there for a reason. Use them. While “All Items” is a fine way to present a list of well, all items, it’s hardly sufficient to present a list of servers built before the Y2K bug hit. You’ll be scrolling the list for hours finally arriving at Page 387 of 12,591 and cursing that SharePoint guy for convincing you that putting your hardware into a list would be of any use to anyone. Next to collecting the data, presenting it is just as important. Views are often overlooked and many times ignored or misused. They’re the way you can slice and dice the data up so that you’re not trying to consume 3,000 years of human evolution on a single web page. Remember views can be filtered so feel free to create a view for each status or one for each operating system or one for each species of Information Worker you might be putting in that list or document library. Not only will it reduce the number of items someone sees at one time, it’ll also make the information that much more relevant. Also remember that each view is a separate page. Use it in navigation by creating a menu on the Quick Launch to each view. The discoverability of the Views menu isn’t overly obvious and if you violate the rule of columns (see Horizontally Scrolling below) the view menu doesn’t even show up until you shuffle the scroll bar to the left. Navigation links, big giant buttons, a screaming flashing “CLICK ME NOW” will help your users find their way. Sort It! Views are great so we’re building nice, rich views for the user. Awesomesauce. However sort is not very discoverable by the user. For example when you’re looking at a view how do you know if it’s ascending or descending and what is it sorted on. Maybe it’s sorted using two fields so what’s that all about? Help your users by letting them know the information they’re looking at is sorted. Maybe you name the view something appropriate like “Bogus Expense Claims Sorted By Deadbeats”. If you use the naming strategy just make sure you keep the name consistent with the description. In the previous example their better be a Deadbeat column so I can see the sort in action. Having a “Loser” column, while equally correct, is a little obtuse to the average Information Worker. Remember, they usually don’t use acronyms and even if they knew how to, it’s not immediately obvious to them that’s what you’re trying to convey. Another option is to simply drop a Content Editor Web Part above the list and explain exactly the view they’re looking at. Each view is it’s own page so one CEWP won’t be used across the board. Be descriptive in what the user is seeing but try to keep it brief. Dumping the first chapter of I, Claudius might be informative to the data but can gobble up screen real estate and miss the point of having the list. DO NOT Useless Attachments The attachments column is, in a word, useless. For the most part. Sure it indicates there’s an attachment on the list item but in the grand scheme of things that’s not overly informative. Maybe it is and by all means, if it makes sense to you include it. Colour it. Make it shine and stand like the Return of Clippy on every SharePoint list. Without it being functional it can be boring. EndUserSharePoint.com has an article to make the son of Clippy that much more useful so feel free to head over and check out this blog post by Paul Grenier on the task (Warning code ahead! Danger Will Robinson!) In any case, I would suggest you remove it from your views. Again if it’s important then include it but consider the jQuery solution above to make it functional. It’s added by default to views and one of things that people forget to clean up. Horizontal Scrolling Screen real estate is premium so building a list that contains 8,000 columns and stretches horizontally across 15 screens probably isn’t the most user friendly experience. Most users can’t figure out how to scroll vertically let alone horizontally so don’t make it even that more confusing for them. Take the Steve Krug approach in your view designs and try not to make the user think. Again views are your friend. Consider splitting up the data into views where one view contains 10 columns and other view contains the other 10. Okay, maybe your information doesn’t work that way but humans can only process 7 pieces of data at a time, 10 at most (then their heads explode and you don’t want to clean that mess up, especially on a Friday night before the big dance). It drives me batshit crazy when I see a view with 80 columns of data. I often ask the user “So what do you do with all this information”. The response is usually “With this data [the first 10 columns] I decide if I’m going to fire everyone, and with this data [the next 10 columns] I decide if I’m going to set the building on fire and collect the insurance”. It’s at that point I show them how to create two new views “People Who Are About To Get The Axe” and “Beach Time For The Executives”. Again, talk to your users and try to reason with them on cutting down the number of columns they see at once. Vertical Scrolling Another big faux pas I find is the use of multi-line comment fields in views. It’s not so bad when you have a statement like this in your view: “I really like, oh my god, thought I was going to scream when I saw this turtle then I decided what I was going to have for dinner and frankly I hate having to work late so when I was talking to the customer I thought, oh my god, what if the customer has turtles and then it appeared to me that I really was hungry so I'm going to have lunch now.” It’s fine if that’s the only column along with two or three others, but once you slap those 20 columns of data into the list, the comment field wraps and forms a new multi-page novel that takes up your entire screen. Do everyone a favour and just avoid adding the column to views. Train the user to just click through to the item if they need to see the contents. Duplicate Information Duplication is never good. Views and great as you can group data together. For example create a view of project status reports grouped by author. Then you can see what project manager is being a dip and not submitting their report. However if you group by author do you really need the Created By field as well in the view? Or if the view is grouped by Project then Author do you need both. Horizontal real estate is always at a premium so try not to clutter up the view with duplicate data like this. Oh  yeah, if you’re scratching your head saying “But Bil, if I don’t include the Project name in the view and I have a lot of items then how do I know which one I’m looking at”. That’s a hint that your grouping is too vague or you have too much data in the view based on that criteria. Filter it down a notch, create some views, and try to keep the group down to a single screen where you can see the group header at the top of the page. Again it’s just managing the information you have. Redundant, See Redundant This partially relates to duplicate information and smart columns but basically remember to not include the obvious in a view. Remember, don’t make me think. If you’ve gone to the trouble (and it was a lot of trouble wasn’t it?) to create separate views of your data by creating a “September Zombie Brain Sales”, “October Zombie Brain Sales”, etc. then please for the love of all that is holy do not include the Month and Product columns in your view. Similarly if you create a “My” view of anything (“My Favourite Brands of Spandex”, “My Co-Workers I Find The Urge To Disinfect”) then again, do not include the owner or author field (or whatever field you use to identify “My”). That’s just silly. Hope that helps! Happy customizing!

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• Architecture a for a central renderer rather than self-rendering

  - by The Communist Duck

  For the architectural side of rendering, there's two main ways: having each object render itself, and having a single renderer which renders everything. I'm currently aiming for the second idea, for the following reasons: The list can be sorted to only use shaders once. Else each object would have to bind the shader, because it's not sure if it's active. The objects could be sorted and grouped. Easier to swap APIs. With a few macro lines, it can be easy to swap between a DirectX renderer and an OpenGL renderer (not a reason for my project, but still a good point) Easier to manage rendering code Of course, if anyone has strong recommendations for the first method, I will listen to them. But I was wondering how make this work. First idea The renderer has a list of pointers to the renderable components of each entity, which register themselves on RenderCompoent creation. However, I'm worrying that this may end up as a lot of extra pointer weight. But I can sort the list of pointers every so often. Second idea The entire list of entities is passed to the renderer each render call. The renderer then sorts the list (each call, or maybe once?) and gets what it wants. That's a lot of passing and/or sorting, however. Other ideas ??? PROFIT Anyone got ideas? Thank you.

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• Get 100 highest numbers from an infinite list

  - by Sachin Shanbhag

  One of my friend was asked this interview question - "There is a constant flow of numbers coming in from some infinite list of numbers out of which you need to maintain a datastructure as to return the top 100 highest numbers at any given point of time. Assume all the numbers are whole numbers only." This is simple, you need to keep a sorted list in descending order and keep a track on lowest number in that list. If new number obtained is greater than that lowest number then you have to remove that lowest number and insert the new number in sorted list as required. Then question was extended - "Can you make sure that the Order for insertion should be O(1)? Is it possible?" As far as I knew, even if you add a new number to list and sort it again using any sort algorithm, it would by best be O(logn) for quicksort (I think). So my friend told it was not possible. But he was not convinced, he asked to maintain any other data structure rather than a list. I thought of balanced Binary tree, but even there you will not get the insertion with order of 1. So the same question I have too now. Wanted to know if there is any such data structure which can do insertion in Order of 1 for above problem or it is not possible at all.

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• Testing a codebase with sequential cohesion

  - by iveqy

  I've this really simple program written in C with ncurses that's basically a front-end to sqlite3. I would like to implement TDD to continue the development and have found a nice C unit framework for this. However I'm totally stuck on how to implement it. Take this case for example: A user types a letter 'l' that is captured by ncurses getch(), and then an sqlite3 query is run that for every row calls a callback function. This callback function prints stuff to the screen via ncurses. So the obvious way to fully test this is to simulate a keyboard and a terminal and make sure that the output is the expected. However this sounds too complicated. I was thinking about adding an abstraction layer between the database and the UI so that the callback function will populate a list of entries and that list will later be printed. In that case I would be able to check if that list contains the expected values. However, why would I struggle with a data structure and lists in my program when sqlite3 already does this? For example, if the user wants to see the list sorted in some other way, it would be expensive to throw away the list and repopulate it. I would need to sort the list, but why should I implement sorting when sqlite3 already has that? Using my orginal design I could just do an other query sorted differently. Previously I've only done TDD with command line applications, and there it's really easy to just compare the output with what I'm expected. An other way would be to add CLI interface to the program and wrap a test program around the CLI to test everything. (The way git.git does with it's test-framework). So the question is, how to add testing to a tightly integrated database/UI.

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• Sorting in Hash Maps in Java

  - by Crystal

  I'm trying to get familiar with Collections. I have a String which is my key, email address, and a Person object (firstName, lastName, telephone, email). I read in the Java collections chapter on Sun's webpages that if you had a HashMap and wanted it sorted, you could use a TreeMap. How does this sort work? Is it based on the compareTo() method you have in your Person class? I overrode the compareTo() method in my Person class to sort by lastName. But it isn't working properly and was wondering if I have the right idea or not. getSortedListByLastName at the bottom of this code is where I try to convert to a TreeMap. Also, if this is the correct way to do it, or one of the correct ways to do it, how do I then sort by firstName since my compareTo() is comparing by lastName. import java.util.*; public class OrganizeThis { /** Add a person to the organizer @param p A person object */ public void add(Person p) { staff.put(p.getEmail(), p); //System.out.println("Person " + p + "added"); } /** * Remove a Person from the organizer. * * @param email The email of the person to be removed. */ public void remove(String email) { staff.remove(email); } /** * Remove all contacts from the organizer. * */ public void empty() { staff.clear(); } /** * Find the person stored in the organizer with the email address. * Note, each person will have a unique email address. * * @param email The person email address you are looking for. * */ public Person findByEmail(String email) { Person aPerson = staff.get(email); return aPerson; } /** * Find all persons stored in the organizer with the same last name. * Note, there can be multiple persons with the same last name. * * @param lastName The last name of the persons your are looking for. * */ public Person[] find(String lastName) { ArrayList<Person> names = new ArrayList<Person>(); for (Person s : staff.values()) { if (s.getLastName() == lastName) { names.add(s); } } // Convert ArrayList back to Array Person nameArray[] = new Person[names.size()]; names.toArray(nameArray); return nameArray; } /** * Return all the contact from the orgnizer in * an array sorted by last name. * * @return An array of Person objects. * */ public Person[] getSortedListByLastName() { Map<String, Person> sorted = new TreeMap<String, Person>(staff); ArrayList<Person> sortedArrayList = new ArrayList<Person>(); for (Person s: sorted.values()) { sortedArrayList.add(s); } Person sortedArray[] = new Person[sortedArrayList.size()]; sortedArrayList.toArray(sortedArray); return sortedArray; } private Map<String, Person> staff = new HashMap<String, Person>(); public static void main(String[] args) { OrganizeThis testObj = new OrganizeThis(); Person person1 = new Person("J", "W", "111-222-3333", "[email protected]"); Person person2 = new Person("K", "W", "345-678-9999", "[email protected]"); Person person3 = new Person("Phoebe", "Wang", "322-111-3333", "[email protected]"); Person person4 = new Person("Nermal", "Johnson", "322-342-5555", "[email protected]"); Person person5 = new Person("Apple", "Banana", "123-456-1111", "[email protected]"); testObj.add(person1); testObj.add(person2); testObj.add(person3); testObj.add(person4); testObj.add(person5); System.out.println(testObj.findByEmail("[email protected]")); System.out.println("------------" + '\n'); Person a[] = testObj.find("W"); for (Person p : a) System.out.println(p); System.out.println("------------" + '\n'); a = testObj.find("W"); for (Person p : a) System.out.println(p); System.out.println("SORTED" + '\n'); a = testObj.getSortedListByLastName(); for (Person b : a) { System.out.println(b); } } } Person class: public class Person implements Comparable { String firstName; String lastName; String telephone; String email; public Person() { firstName = ""; lastName = ""; telephone = ""; email = ""; } public Person(String firstName) { this.firstName = firstName; } public Person(String firstName, String lastName, String telephone, String email) { this.firstName = firstName; this.lastName = lastName; this.telephone = telephone; this.email = email; } public String getFirstName() { return firstName; } public void setFirstName(String firstName) { this.firstName = firstName; } public String getLastName() { return lastName; } public void setLastName(String lastName) { this.lastName = lastName; } public String getTelephone() { return telephone; } public void setTelephone(String telephone) { this.telephone = telephone; } public String getEmail() { return email; } public void setEmail(String email) { this.email = email; } public int compareTo(Object o) { String s1 = this.lastName + this.firstName; String s2 = ((Person) o).lastName + ((Person) o).firstName; return s1.compareTo(s2); } public boolean equals(Object otherObject) { // a quick test to see if the objects are identical if (this == otherObject) { return true; } // must return false if the explicit parameter is null if (otherObject == null) { return false; } if (!(otherObject instanceof Person)) { return false; } Person other = (Person) otherObject; return firstName.equals(other.firstName) && lastName.equals(other.lastName) && telephone.equals(other.telephone) && email.equals(other.email); } public int hashCode() { return this.email.toLowerCase().hashCode(); } public String toString() { return getClass().getName() + "[firstName = " + firstName + '\n' + "lastName = " + lastName + '\n' + "telephone = " + telephone + '\n' + "email = " + email + "]"; } }

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• Using VLOOKUP in Excel

  - by Mark Virtue

  VLOOKUP is one of Excel’s most useful functions, and it’s also one of the least understood.  In this article, we demystify VLOOKUP by way of a real-life example.  We’ll create a usable Invoice Template for a fictitious company. So what is VLOOKUP?  Well, of course it’s an Excel function.  This article will assume that the reader already has a passing understanding of Excel functions, and can use basic functions such as SUM, AVERAGE, and TODAY.  In its most common usage, VLOOKUP is a database function, meaning that it works with database tables – or more simply, lists of things in an Excel worksheet.  What sort of things?   Well, any sort of thing.  You may have a worksheet that contains a list of employees, or products, or customers, or CDs in your CD collection, or stars in the night sky.  It doesn’t really matter. Here’s an example of a list, or database.  In this case it’s a list of products that our fictitious company sells: Usually lists like this have some sort of unique identifier for each item in the list.  In this case, the unique identifier is in the “Item Code” column.  Note:  For the VLOOKUP function to work with a database/list, that list must have a column containing the unique identifier (or “key”, or “ID”), and that column must be the first column in the table.  Our sample database above satisfies this criterion. The hardest part of using VLOOKUP is understanding exactly what it’s for.  So let’s see if we can get that clear first: VLOOKUP retrieves information from a database/list based on a supplied instance of the unique identifier. Put another way, if you put the VLOOKUP function into a cell and pass it one of the unique identifiers from your database, it will return you one of the pieces of information associated with that unique identifier.  In the example above, you would pass VLOOKUP an item code, and it would return to you either the corresponding item’s description, its price, or its availability (its “In stock” quantity).  Which of these pieces of information will it pass you back?  Well, you get to decide this when you’re creating the formula. If all you need is one piece of information from the database, it would be a lot of trouble to go to to construct a formula with a VLOOKUP function in it.  Typically you would use this sort of functionality in a reusable spreadsheet, such as a template.  Each time someone enters a valid item code, the system would retrieve all the necessary information about the corresponding item. Let’s create an example of this:  An Invoice Template that we can reuse over and over in our fictitious company. First we start Excel… …and we create ourselves a blank invoice: This is how it’s going to work:  The person using the invoice template will fill in a series of item codes in column “A”, and the system will retrieve each item’s description and price, which will be used to calculate the line total for each item (assuming we enter a valid quantity). For the purposes of keeping this example simple, we will locate the product database on a separate sheet in the same workbook: In reality, it’s more likely that the product database would be located in a separate workbook.  It makes little difference to the VLOOKUP function, which doesn’t really care if the database is located on the same sheet, a different sheet, or a completely different workbook. In order to test the VLOOKUP formula we’re about to write, we first enter a valid item code into cell A11: Next, we move the active cell to the cell in which we want information retrieved from the database by VLOOKUP to be stored.  Interestingly, this is the step that most people get wrong.  To explain further:  We are about to create a VLOOKUP formula that will retrieve the description that corresponds to the item code in cell A11.  Where do we want this description put when we get it?  In cell B11, of course.  So that’s where we write the VLOOKUP formula – in cell B11. Select cell B11: We need to locate the list of all available functions that Excel has to offer, so that we can choose VLOOKUP and get some assistance in completing the formula.  This is found by first clicking the Formulas tab, and then clicking Insert Function:   A box appears that allows us to select any of the functions available in Excel.  To find the one we’re looking for, we could type a search term like “lookup” (because the function we’re interested in is a lookup function).  The system would return us a list of all lookup-related functions in Excel.  VLOOKUP is the second one in the list.  Select it an click OK… The Function Arguments box appears, prompting us for all the arguments (or parameters) needed in order to complete the VLOOKUP function.  You can think of this box as the function is asking us the following questions: What unique identifier are you looking up in the database? Where is the database? Which piece of information from the database, associated with the unique identifier, do you wish to have retrieved for you? The first three arguments are shown in bold, indicating that they are mandatory arguments (the VLOOKUP function is incomplete without them and will not return a valid value).  The fourth argument is not bold, meaning that it’s optional:   We will complete the arguments in order, top to bottom. The first argument we need to complete is the Lookup_value argument.  The function needs us to tell it where to find the unique identifier (the item code in this case) that it should be retuning the description of.  We must select the item code we entered earlier (in A11). Click on the selector icon to the right of the first argument: Then click once on the cell containing the item code (A11), and press Enter: The value of “A11” is inserted into the first argument. Now we need to enter a value for the Table_array argument.  In other words, we need to tell VLOOKUP where to find the database/list.  Click on the selector icon next to the second argument: Now locate the database/list and select the entire list – not including the header line.  The database is located on a separate worksheet, so we first click on that worksheet tab: Next we select the entire database, not including the header line: …and press Enter.  The range of cells that represents the database (in this case “’Product Database’!A2:D7”) is entered automatically for us into the second argument. Now we need to enter the third argument, Col_index_num.  We use this argument to specify to VLOOKUP which piece of information from the database, associate with our item code in A11, we wish to have returned to us.  In this particular example, we wish to have the item’s description returned to us.  If you look on the database worksheet, you’ll notice that the “Description” column is the second column in the database.  This means that we must enter a value of “2” into the Col_index_num box: It is important to note that that we are not entering a “2” here because the “Description” column is in the B column on that worksheet.  If the database happened to start in column K of the worksheet, we would still enter a “2” in this field. Finally, we need to decide whether to enter a value into the final VLOOKUP argument, Range_lookup.  This argument requires either a true or false value, or it should be left blank.  When using VLOOKUP with databases (as is true 90% of the time), then the way to decide what to put in this argument can be thought of as follows: If the first column of the database (the column that contains the unique identifiers) is sorted alphabetically/numerically in ascending order, then it’s possible to enter a value of true into this argument, or leave it blank. If the first column of the database is not sorted, or it’s sorted in descending order, then you must enter a value of false into this argument As the first column of our database is not sorted, we enter false into this argument: That’s it!  We’ve entered all the information required for VLOOKUP to return the value we need.  Click the OK button and notice that the description corresponding to item code “R99245” has been correctly entered into cell B11: The formula that was created for us looks like this: If we enter a different item code into cell A11, we will begin to see the power of the VLOOKUP function:  The description cell changes to match the new item code: We can perform a similar set of steps to get the item’s price returned into cell E11.  Note that the new formula must be created in cell E11.  The result will look like this: …and the formula will look like this: Note that the only difference between the two formulae is the third argument (Col_index_num) has changed from a “2” to a “3” (because we want data retrieved from the 3rd column in the database). If we decided to buy 2 of these items, we would enter a “2” into cell D11.  We would then enter a simple formula into cell F11 to get the line total: =D11*E11 …which looks like this… Completing the Invoice Template We’ve learned a lot about VLOOKUP so far.  In fact, we’ve learned all we’re going to learn in this article.  It’s important to note that VLOOKUP can be used in other circumstances besides databases.  This is less common, and may be covered in future How-To Geek articles. Our invoice template is not yet complete.  In order to complete it, we would do the following: We would remove the sample item code from cell A11 and the “2” from cell D11.  This will cause our newly created VLOOKUP formulae to display error messages: We can remedy this by judicious use of Excel’s IF() and ISBLANK() functions.  We change our formula from this…       =VLOOKUP(A11,’Product Database’!A2:D7,2,FALSE) …to this…       =IF(ISBLANK(A11),”",VLOOKUP(A11,’Product Database’!A2:D7,2,FALSE)) We would copy the formulas in cells B11, E11 and F11 down to the remainder of the item rows of the invoice.  Note that if we do this, the resulting formulas will no longer correctly refer to the database table.  We could fix this by changing the cell references for the database to absolute cell references.  Alternatively – and even better – we could create a range name for the entire product database (such as “Products”), and use this range name instead of the cell references.  The formula would change from this…       =IF(ISBLANK(A11),”",VLOOKUP(A11,’Product Database’!A2:D7,2,FALSE)) …to this…       =IF(ISBLANK(A11),”",VLOOKUP(A11,Products,2,FALSE)) …and then copy the formulas down to the rest of the invoice item rows. We would probably “lock” the cells that contain our formulae (or rather unlock the other cells), and then protect the worksheet, in order to ensure that our carefully constructed formulae are not accidentally overwritten when someone comes to fill in the invoice. We would save the file as a template, so that it could be reused by everyone in our company If we were feeling really clever, we would create a database of all our customers in another worksheet, and then use the customer ID entered in cell F5 to automatically fill in the customer’s name and address in cells B6, B7 and B8. If you would like to practice with VLOOKUP, or simply see our resulting Invoice Template, it can be downloaded from here. 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• C#/.NET Little Wonders: The Useful But Overlooked Sets

  - by James Michael Hare

  Once again we consider some of the lesser known classes and keywords of C#.  Today we will be looking at two set implementations in the System.Collections.Generic namespace: HashSet<T> and SortedSet<T>.  Even though most people think of sets as mathematical constructs, they are actually very useful classes that can be used to help make your application more performant if used appropriately. A Background From Math In mathematical terms, a set is an unordered collection of unique items.  In other words, the set {2,3,5} is identical to the set {3,5,2}.  In addition, the set {2, 2, 4, 1} would be invalid because it would have a duplicate item (2).  In addition, you can perform set arithmetic on sets such as: Intersections: The intersection of two sets is the collection of elements common to both.  Example: The intersection of {1,2,5} and {2,4,9} is the set {2}. Unions: The union of two sets is the collection of unique items present in either or both set.  Example: The union of {1,2,5} and {2,4,9} is {1,2,4,5,9}. Differences: The difference of two sets is the removal of all items from the first set that are common between the sets.  Example: The difference of {1,2,5} and {2,4,9} is {1,5}. Supersets: One set is a superset of a second set if it contains all elements that are in the second set. Example: The set {1,2,5} is a superset of {1,5}. Subsets: One set is a subset of a second set if all the elements of that set are contained in the first set. Example: The set {1,5} is a subset of {1,2,5}. If We’re Not Doing Math, Why Do We Care? Now, you may be thinking: why bother with the set classes in C# if you have no need for mathematical set manipulation?  The answer is simple: they are extremely efficient ways to determine ownership in a collection. For example, let’s say you are designing an order system that tracks the price of a particular equity, and once it reaches a certain point will trigger an order.  Now, since there’s tens of thousands of equities on the markets, you don’t want to track market data for every ticker as that would be a waste of time and processing power for symbols you don’t have orders for.  Thus, we just want to subscribe to the stock symbol for an equity order only if it is a symbol we are not already subscribed to. Every time a new order comes in, we will check the list of subscriptions to see if the new order’s stock symbol is in that list.  If it is, great, we already have that market data feed!  If not, then and only then should we subscribe to the feed for that symbol. So far so good, we have a collection of symbols and we want to see if a symbol is present in that collection and if not, add it.  This really is the essence of set processing, but for the sake of comparison, let’s say you do a list instead: 1: // class that handles are order processing service 2: public sealed class OrderProcessor 3: { 4: // contains list of all symbols we are currently subscribed to 5: private readonly List<string> _subscriptions = new List<string>(); 6:  7: ... 8: } Now whenever you are adding a new order, it would look something like: 1: public PlaceOrderResponse PlaceOrder(Order newOrder) 2: { 3: // do some validation, of course... 4:  5: // check to see if already subscribed, if not add a subscription 6: if (!_subscriptions.Contains(newOrder.Symbol)) 7: { 8: // add the symbol to the list 9: _subscriptions.Add(newOrder.Symbol); 10: 11: // do whatever magic is needed to start a subscription for the symbol 12: } 13:  14: // place the order logic! 15: } What’s wrong with this?  In short: performance!  Finding an item inside a List<T> is a linear - O(n) – operation, which is not a very performant way to find if an item exists in a collection. (I used to teach algorithms and data structures in my spare time at a local university, and when you began talking about big-O notation you could immediately begin to see eyes glossing over as if it was pure, useless theory that would not apply in the real world, but I did and still do believe it is something worth understanding well to make the best choices in computer science). Let’s think about this: a linear operation means that as the number of items increases, the time that it takes to perform the operation tends to increase in a linear fashion.  Put crudely, this means if you double the collection size, you might expect the operation to take something like the order of twice as long.  Linear operations tend to be bad for performance because they mean that to perform some operation on a collection, you must potentially “visit” every item in the collection.  Consider finding an item in a List<T>: if you want to see if the list has an item, you must potentially check every item in the list before you find it or determine it’s not found. Now, we could of course sort our list and then perform a binary search on it, but sorting is typically a linear-logarithmic complexity – O(n * log n) - and could involve temporary storage.  So performing a sort after each add would probably add more time.  As an alternative, we could use a SortedList<TKey, TValue> which sorts the list on every Add(), but this has a similar level of complexity to move the items and also requires a key and value, and in our case the key is the value. This is why sets tend to be the best choice for this type of processing: they don’t rely on separate keys and values for ordering – so they save space – and they typically don’t care about ordering – so they tend to be extremely performant.  The .NET BCL (Base Class Library) has had the HashSet<T> since .NET 3.5, but at that time it did not implement the ISet<T> interface.  As of .NET 4.0, HashSet<T> implements ISet<T> and a new set, the SortedSet<T> was added that gives you a set with ordering. HashSet<T> – For Unordered Storage of Sets When used right, HashSet<T> is a beautiful collection, you can think of it as a simplified Dictionary<T,T>.  That is, a Dictionary where the TKey and TValue refer to the same object.  This is really an oversimplification, but logically it makes sense.  I’ve actually seen people code a Dictionary<T,T> where they store the same thing in the key and the value, and that’s just inefficient because of the extra storage to hold both the key and the value. As it’s name implies, the HashSet<T> uses a hashing algorithm to find the items in the set, which means it does take up some additional space, but it has lightning fast lookups!  Compare the times below between HashSet<T> and List<T>: Operation HashSet<T> List<T> Add() O(1) O(1) at end O(n) in middle Remove() O(1) O(n) Contains() O(1) O(n)   Now, these times are amortized and represent the typical case.  In the very worst case, the operations could be linear if they involve a resizing of the collection – but this is true for both the List and HashSet so that’s a less of an issue when comparing the two. The key thing to note is that in the general case, HashSet is constant time for adds, removes, and contains!  This means that no matter how large the collection is, it takes roughly the exact same amount of time to find an item or determine if it’s not in the collection.  Compare this to the List where almost any add or remove must rearrange potentially all the elements!  And to find an item in the list (if unsorted) you must search every item in the List. So as you can see, if you want to create an unordered collection and have very fast lookup and manipulation, the HashSet is a great collection. And since HashSet<T> implements ICollection<T> and IEnumerable<T>, it supports nearly all the same basic operations as the List<T> and can use the System.Linq extension methods as well. All we have to do to switch from a List<T> to a HashSet<T>  is change our declaration.  Since List and HashSet support many of the same members, chances are we won’t need to change much else. 1: public sealed class OrderProcessor 2: { 3: private readonly HashSet<string> _subscriptions = new HashSet<string>(); 4:  5: // ... 6:  7: public PlaceOrderResponse PlaceOrder(Order newOrder) 8: { 9: // do some validation, of course... 10: 11: // check to see if already subscribed, if not add a subscription 12: if (!_subscriptions.Contains(newOrder.Symbol)) 13: { 14: // add the symbol to the list 15: _subscriptions.Add(newOrder.Symbol); 16: 17: // do whatever magic is needed to start a subscription for the symbol 18: } 19: 20: // place the order logic! 21: } 22:  23: // ... 24: } 25: Notice, we didn’t change any code other than the declaration for _subscriptions to be a HashSet<T>.  Thus, we can pick up the performance improvements in this case with minimal code changes. SortedSet<T> – Ordered Storage of Sets Just like HashSet<T> is logically similar to Dictionary<T,T>, the SortedSet<T> is logically similar to the SortedDictionary<T,T>. The SortedSet can be used when you want to do set operations on a collection, but you want to maintain that collection in sorted order.  Now, this is not necessarily mathematically relevant, but if your collection needs do include order, this is the set to use. So the SortedSet seems to be implemented as a binary tree (possibly a red-black tree) internally.  Since binary trees are dynamic structures and non-contiguous (unlike List and SortedList) this means that inserts and deletes do not involve rearranging elements, or changing the linking of the nodes.  There is some overhead in keeping the nodes in order, but it is much smaller than a contiguous storage collection like a List<T>.  Let’s compare the three: Operation HashSet<T> SortedSet<T> List<T> Add() O(1) O(log n) O(1) at end O(n) in middle Remove() O(1) O(log n) O(n) Contains() O(1) O(log n) O(n)   The MSDN documentation seems to indicate that operations on SortedSet are O(1), but this seems to be inconsistent with its implementation and seems to be a documentation error.  There’s actually a separate MSDN document (here) on SortedSet that indicates that it is, in fact, logarithmic in complexity.  Let’s put it in layman’s terms: logarithmic means you can double the collection size and typically you only add a single extra “visit” to an item in the collection.  Take that in contrast to List<T>’s linear operation where if you double the size of the collection you double the “visits” to items in the collection.  This is very good performance!  It’s still not as performant as HashSet<T> where it always just visits one item (amortized), but for the addition of sorting this is a good thing. Consider the following table, now this is just illustrative data of the relative complexities, but it’s enough to get the point: Collection Size O(1) Visits O(log n) Visits O(n) Visits 1 1 1 1 10 1 4 10 100 1 7 100 1000 1 10 1000   Notice that the logarithmic – O(log n) – visit count goes up very slowly compare to the linear – O(n) – visit count.  This is because since the list is sorted, it can do one check in the middle of the list, determine which half of the collection the data is in, and discard the other half (binary search).  So, if you need your set to be sorted, you can use the SortedSet<T> just like the HashSet<T> and gain sorting for a small performance hit, but it’s still faster than a List<T>. Unique Set Operations Now, if you do want to perform more set-like operations, both implementations of ISet<T> support the following, which play back towards the mathematical set operations described before: IntersectWith() – Performs the set intersection of two sets.  Modifies the current set so that it only contains elements also in the second set. UnionWith() – Performs a set union of two sets.  Modifies the current set so it contains all elements present both in the current set and the second set. ExceptWith() – Performs a set difference of two sets.  Modifies the current set so that it removes all elements present in the second set. IsSupersetOf() – Checks if the current set is a superset of the second set. IsSubsetOf() – Checks if the current set is a subset of the second set. For more information on the set operations themselves, see the MSDN description of ISet<T> (here). What Sets Don’t Do Don’t get me wrong, sets are not silver bullets.  You don’t really want to use a set when you want separate key to value lookups, that’s what the IDictionary implementations are best for. Also sets don’t store temporal add-order.  That is, if you are adding items to the end of a list all the time, your list is ordered in terms of when items were added to it.  This is something the sets don’t do naturally (though you could use a SortedSet with an IComparer with a DateTime but that’s overkill) but List<T> can. Also, List<T> allows indexing which is a blazingly fast way to iterate through items in the collection.  Iterating over all the items in a List<T> is generally much, much faster than iterating over a set. Summary Sets are an excellent tool for maintaining a lookup table where the item is both the key and the value.  In addition, if you have need for the mathematical set operations, the C# sets support those as well.  The HashSet<T> is the set of choice if you want the fastest possible lookups but don’t care about order.  In contrast the SortedSet<T> will give you a sorted collection at a slight reduction in performance.   Technorati Tags: C#,.Net,Little Wonders,BlackRabbitCoder,ISet,HashSet,SortedSet

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• Sorting eigenvectors by their eigenvalues (associated sorting)

  - by fbrereto

  I have an unsorted vector of eigenvalues and a related matrix of eigenvectors. I'd like to sort the columns of the matrix with respect to the sorted set of eigenvalues. (e.g., if eigenvalue[3] moves to eigenvalue[2], I want column 3 of the eigenvector matrix to move over to column 2.) I know I can sort the eigenvalues in O(N log N) via std::sort. Without rolling my own sorting algorithm, how do I make sure the matrix's columns (the associated eigenvectors) follow along with their eigenvalues as the latter are sorted?

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• Suitable GUI for sorting rows at database level and/or WYSIWYG level?

  - by Kristoffer

  Consider an Explorer-like list view with a number of columns. The data is fetched from a database, and the rows can be sorted by clicking the column headers. When you click column A, you expect the fetched data to be sorted by A - at the database level ("ORDER BY" at the selected column). However, sometimes it is desirable to sort the data presented in the GUI - the visible data (WYSIWYG). How do you combine these two? E.g. How do you allow the user to sort both the fetched data and the data visible in the GUI? Have you seen a GUI that solves this elegantly?

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• Indexing vs. no indexing when inserting records

  - by jbu

  I have a few questions about whether or not it would be best to not use indexing. BACKGROUND: My records have a timestamp attribute, and the records will be inserted in order of their timestamps (i.e., inserted chronologically). QUESTIONS: If I DON'T use indexing is it typical for the database to insert the records in the order that they were inserted? If answer to #1 is yes, when I do a "SELECT .. WHERE timestamp X" type query will the database be efficient at it, or will it have to go through every single record since it isn't indexed? I would assume if there were no index, the database would not "know" that the records were inserted in sorted order and could not, therefore, make use of sorted property of the database. I assume a clustered index would be best for these types of records & their inserts. Please let me know what you guys think. Thanks, jbu

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• multicolumn sorting of WinForms DataGridView

  - by Bi

  I have a DataGridView in a windows form with 3 columns: Serial number, Name, and Date-Time. The Name column will always have either of the two values: "name1" or "name2". I need to sort these columns such that the grid displays all the rows with name values in a specific order (first display all the "name1" rows and then all the "name2" rows). Within the "name1" rows, I want the rows to be sorted by the Date-Time. Please note programmatically, all the 3 columns are strings. For example, if I have the rows: 01 |Name1 | 2010-05-05 10:00 PM 02 |Name2 | 2010-05-02 08:00 AM 03 |Name2 | 2010-05-01 08:00 AM 04 |Name1 | 2010-05-01 11:00 AM 05 |Name1 | 2010-05-04 07:00 AM needs to be sorted as 04 |Name1 | 2010-05-01 11:00 AM 05 |Name1 | 2010-05-04 07:00 AM 01 |Name1 | 2010-05-05 10:00 PM 03 |Name2 | 2010-05-01 08:00 AM 02 |Name2 | 2010-05-02 08:00 AM I am not sure how to go about using the below: myGrid.Sort(.....,ListSortDirection.Ascending)

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• How do I sort a hash table in javascript?

  - by Colen

  I have a javascript hash table, like so: var things = [ ]; things["hello"] = {"name" : "zzz I fell asleep", "number" : 7}; things["one"] = {"name" : "something", "number" : 18}; things["two"] = {"name" : "another thing", "number" : -2}; I want to sort these into order by name, so if I iterate through the hash table it will go in order another thing something zzz I fell asleep I tried doing this: function compareThings(thing1, thing2) { var name1 = thing1["name"].toLowerCase(); var name2 = thing2["name"].toLowerCase(); if (name1 < name2) { return -1; } if (name1 > name2) { return 1; } return 0; } things.sort(compareThings); But it doesn't seem to work. Edit: it occurs to me that perhaps a sorted hash table is an oxymoron. If so, what's the best way to get access to a sorted list of the things here?

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• Efficient set intersection algorithm

  - by David

  Given two lists (not necessarily sorted), what is the most efficient non-recursive algorithm to find the intersection of those lists?

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• PyQt: How to keep QTreeView nodes correctly expanded after a sort

  - by taynaron

  I'm writing a simple test program using QTreeModel and QTreeView for a more complex project later on. In this simple program, I have data in groups which may be contracted or expanded, as one would expect in a QTreeView. The data may also be sorted by the various data columns (QTreeView.setSortingEnabled is True). Each tree item is a list of data, so the sort function implemented in the TreeModel class uses the built-in python list sort: self.layoutAboutToBeChanged.emit() self.rootItem.childItems.sort(key=lambda x: x.itemData[col], reverse=order) for item in self.rootItem.childItems: item.childItems.sort(key=lambda x: x.itemData[col], reverse=order) self.layoutChanged.emit() The problem is that whenever I change the sorting of the root's child items (the tree is only 2 levels deep, so this is the only level with children) the nodes aren't necessarily expanded as they were before. If I change the sorting back without expanding or collapsing anything, the nodes are expanded as before the sorting change. Can anyone explain to me what I'm doing wrong? I suspect it's something with not properly reassigning QModelIndex with the sorted nodes, but I'm not sure.

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• Sorting a nodeset before passing to xsl:for-each

  - by Zack Mulgrew

  I have a situation where loop through a sorted nodeset and apply a template on each of the nodes: <div id="contractscontainer"> <xsl:for-each select="document"> <xsl:sort select="content[@name='ClientName']/text()" /> <xsl:apply-templates select="." mode="client-contract" /> </xsl:for-each> </div> I want to do something special with the "first" 5 nodes in the node set and render them nested element. The problem is that they need to be in the same order as if they were sorted (as they are in the loop). I had planned on doing this by using two xsl:for-each elements, each with the correct nodes selected from the set. I can't do this, however, because they need to be sorted before I can select the "first" 5. Example: <div id="contractscontainer"> <div class="first-five"> <xsl:for-each select="document[position() < 6]"> <xsl:sort select="content[@name='ClientName']/text()" /> <xsl:apply-templates select="." mode="client-contract" /> </xsl:for-each> </div> <div class="rest-of-them"> <xsl:for-each select="document[position() > 5]"> <xsl:sort select="content[@name='ClientName']/text()" /> <xsl:apply-templates select="." mode="client-contract" /> </xsl:for-each> </div> </div> I don't think this will work because I'm selecting the nodes by position before sorting them, but I can't use xsl:sort outside of the xsl:for-each. Am I approaching this incorrectly?

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• Sort NSArray of custom objects based on sorting of another NSArray of strings

  - by Nic Hubbard

  I have two NSArray objects that I would like to be sorted the same. One contains NSString objects, the other custom Attribute objects. Here is what my "key" NSArray looks like: // The master order NSArray *stringOrder = [NSArray arrayWithObjects:@"12", @"10", @"2", nil]; The NSArray with custom objects: // The array of custom Attribute objects that I want sorted by the stringOrder array NSMutableArray *items = [[NSMutableArray alloc] init]; Attribute *attribute = nil; attribute = [[Attribute alloc] init]; attribute.assetID = @"10"; [items addObject:attribute]; attribute = [[Attribute alloc] init]; attribute.assetID = @"12"; [items addObject:attribute]; attribute = [[Attribute alloc] init]; attribute.assetID = @"2"; [items addObject:attribute]; So, what I would like to do is use the stringOrder array to determine the sorting of the items array of custom objects. How can I do this?

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• question about merge algorithm

  - by davit-datuashvili

  hi i have question i know that this question is somehow nonsense but let see i have code to merge two sorted array in a one sorted array here is code in java public class Merge { public static void main(String[]args){ int a[]=new int[]{7,14,23,30,35,40}; int b[]=new int[]{5,8,9,11,50,67,81}; int c[]=new int[a.length+b.length]; int al=0; int bl=0; int cl=0; while (al<a.length && bl<b.length) if (a[al]<b[bl]) c[cl++]=a[al++]; else c[cl++]=b[bl++]; while (al<a.length) c[cl++]=a[al++]; while (bl<b.length) c[cl++]=b[bl++]; for (int j=0;j<c.length;j++){ System.out.println(c[j]); } } } question is why does not work if we write here {} brackets while (al } ?

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• Group keywords by site

  - by Skudd

  I am finding a lot of useful help here today, and I really appreciate it. This should be the last one for the day: I have a list of the top 10 keywords per site, sorted by visits, by date. The records need to be sorted as follows (excuse the formatting): 2010-05 2010-04 site1.com keyword1 apples wine keyword1 visits 100 12 keyword2 oranges water keyword2 visits 99 10 site2.com keyword1 blueberry cornbread keyword1 visits 90 100 keyword2 squares biscuits keyword2 visits 80 99 Basically what I need to accomplish involves grouping, but I can't seem to figure it out. Am I heading down the right path, or is there another way to achieve this, or is it just impossible?

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• How to combine elements of a list

  - by Addie

  I'm working in c#. I have a sorted List of structures. The structure has a DateTime object which stores month and year and an integer which stores a value. The list is sorted by date. I need to traverse the list and combine it so that I only have one instance of the structure per date. For example: My initial list would look like this: { (Apr10, 3), (Apr10, 2), (Apr10, -3), (May10, 1), (May10, 1), (May10, -3), (Jun10, 3) } The resulting list should look like this: { (Apr10, 2), (May10, -1), (Jun10, 3) } I'm looking for a simple / efficient solution. The struct is: class CurrentTrade { public DateTime date; public int dwBuy; } The list is: private List<CurrentTrade> FillList

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• Sorting the data returned by a database

  - by Rishabh Ohri

  hi all, In our project we have a requirement that when a set of records are returned by the database the records should be sorted with respect to the TITLE field in the record. The records will have to be sorted alphabetically but if the title of a record has a number in it then it should come after the records whose title only consists of alphabets. Details: we are using SQL Server , and c#. The data from the database comes to an Entity class whic forwards the data to other layers. So, What will be the possible and effective solution for this requirement.

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• The dictionary need to add every word in SpellingMistakes and the line number but it only adds the l

  - by Will Boomsight

  modules import sys import string Importing and reading the files form the Command Prompt Document = open(sys.argv[1],"r") Document = open('Wc.txt', 'r') Document = Document.read().lower() Dictionary = open(sys.argv[2],"r") Dictionary = open('Dict.txt', 'r') Dictionary = Dictionary.read() def Format(Infile): for ch in string.punctuation: Infile = Infile.replace(ch, "") for no in string.digits: Infile = Infile.replace(no, " ") Infile = Infile.lower() return(Infile) def Corrections(Infile, DictWords): Misspelled = set([]) Infile = Infile.split() DictWords = DictWords.splitlines() for word in Infile: if word not in DictWords: Misspelled.add(word) Misspelled = sorted(Misspelled) return (Misspelled) def Linecheck(Infile,ErrorWords): Infile = Infile.split() lineno = 0 Noset = list() for line in Infile: lineno += 1 line = line.split() for word in line: if word == ErrorWords: Noset.append(lineno) sorted(Noset) return(Noset) def addkey(error,linenum): Nodict = {} for line in linenum: Nodict.setdefault(error,[]).append(linenum) return Nodict FormatDoc = Format(Document) SpellingMistakes = Corrections(FormatDoc,Dictionary) alp = str(SpellingMistakes) for word in SpellingMistakes: nSet = str(Linecheck(FormatDoc,word)) nSet = nSet.split() linelist = addkey(word, nSet) print(linelist) # # for word in Nodict.keys(): # Nodict[word].append(line) Prints each incorrect word on a new line

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• In Haskell, how can you sort a list of infinite lists of strings?

  - by HaskellNoob

  So basically, if I have a (finite or infinite) list of (finite or infinite) lists of strings, is it possible to sort the list by length first and then by lexicographic order, excluding duplicates? A sample input/output would be: Input: [["a", "b",...], ["a", "aa", "aaa"], ["b", "bb", "bbb",...], ...] Output: ["a", "b", "aa", "bb", "aaa", "bbb", ...] I know that the input list is not a valid haskell expression but suppose that there is an input like that. I tried using merge algorithm but it tends to hang on the inputs that I give it. Can somebody explain and show a decent sorting function that can do this? If there isn't any function like that, can you explain why? In case somebody didn't understand what I meant by the sorting order, I meant that shortest length strings are sorted first AND if one or more strings are of same length then they are sorted using < operator. Thanks!

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• Is it possible to use array_shift() in PHP and get the key?

  - by alex

  I have a list of files in an array where the filename is the key and the value is the last modified date in seconds. They are sorted from oldest to newest. The files are glob()'d in, and then sorted this way using asort($fileNameToLastModified, SORT_NUMERIC); I use array_shift() to get the oldest file. Unfortunately, it seems to be giving me the value, and there doesn't seem to be a way to get the key. Would the only way to do that be something like this? $keys = array_keys($fileNameToLastModified); $oldest = array_shift($keys); array_shift($fileNameToLastModified); // to manually chop the first array member off too. Or is there a built in? Thanks

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• Is it possible to use array_shift() in PHP and get the key?

  - by alex

  I have a list of files in an array where the filename is the key and the value is the last modified date in seconds. They are sorted from oldest to newest. The files are glob()'d in, and then sorted this way using asort($fileNameToLastModified, SORT_NUMERIC); I use array_shift() to get the oldest file. Unfortunately, it seems to be giving me the value, and there doesn't seem to be a way to get the key. Would the only way to do that be something like this? $keys = array_keys($fileNameToLastModified); $oldest = array_shift($keys); array_shift($fileNameToLastModified); // to manually chop the first array member off too. Or is there a built in? Thanks

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• Sorting a vector of (double precision) reals and obtain their order

  - by Philipp

  Hello everyone, in C++ would like to sort a lengthy (2^20) vector of reals, obviously sort() does the trick. Having used R before I was used to the nice order() function which yields the permutation that leads to the sorted vector. Probably someone has done this in C++, maybe it's just my weak google-Fu that prevents me from finding it. And yeah, obivously my C++ newbness could stop me from spotting something straightforward. Example: x = {24, 55, 22, 1} then the permutation perm = {3, 2, 0, 1} maps the original x to the sorted x in ascending order. I can probably implement some bubble sort which does not only sort x but performs the same transpositions on the vector {0,1,2,...} and outputs both, but I believe someone must have thought about it and especially have done it efficiently. Thank you very much, Philipp

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