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  • Getting list of opened ssh connections by name

    - by lyrae
    I have a config file in my .ssh dir that looks like this Host somehostA HostName 123.45.67.89 User katsh So from my local machine, i can ssh into multiple machines by their name in the config file, like so ssh somehostA ssh somehostB ssh somehostC ... etc Is it possible to get a list of all machines i am connected to, by their name? I know I can do: lsof -i tcp -n | grep '\<ssh\>' and i'll get something like ssh 9871 katsh 3u IPv4 400199 0t0 TCP 987.654.2.2:47329->987.654.2.2:47329:ssh (ESTABLISHED) ssh 20554 katsh 3u IPv4 443965 0t0 TCP 123.456.7.8:41923->123.456.7.8:ssh (ESTABLISHED) But it does not list their names, just IP

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  • IOS not saving evaluate rule in access-list

    - by DeeJay1
    Hi. I have a basic firewall set up on an pretty od IOS in form of IPv6 access list exterior-in6 evaluate exterior-reflect sequence 1 permit ipv6 any host [my external address] sequence 10 permit tcp any host [my internal address] eq 22 sequence 11 permit icmp any any sequence 800 permit udp any any range 6881 6889 sequence 900 permit tcp any any range 6881 6889 sequence 901 deny ipv6 any any sequence 1000 IPv6 access list exterior-out6 permit ipv6 [my internal subnet] any reflect exterior-reflect sequence 10 Unfortunately the evaluate exterior-reflect sequence 1 line seems to get lost after each reboot, leaving my internal network without access. Any ideas?

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  • List all documents (webparts) and sites using a certain solution in sharepoint 2007

    - by tnolan
    I would like to uninstall a Sharepoint application template (GroupBoard Workspace to be exact) but I want to make sure nothing currently relies on it. I don't see any functions within stsadm that will tell me this information and I have even tried SPM which would work, but with such a huge site it's tedious to go through every single web and page to see which features are in use. Is there a way (probably with SQL using the id from stsadm -o enumsolutions) to list everything that relies on a template within a given solution, including webparts on custom pages? If this is not possible, what is the best way to check dependencies prior to uninstalling a solution (especially since GBW is not the only one on my axe list.) Note: I know that stsadm -o deletesolution will stop me from removing something that is in use, but I want to see all of the things that are using a given solution.

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  • How is the Trac Project List page customised?

    - by Completenutter2
    We've been using Trac for a while now for our developers only. However we are now opening it up for our (internal) clients. We have a project listing page (based on the default one that comes with Trac). What we'd like to do, is display more information about the project than what is currently available. I have searched google and here, to see if I can find how to get more information. There seems to be a variable called $project which has .name, .description and .href as attributes. Is there somewhere, a list of the attributes available? Or perhaps a different solution altogether that will allow us to display more information on the project list page. Such as the number of open tickets etc.

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  • Create a dependent drop down list in a single cell in Excel

    - by Larry Anderson
    I am trying to create a dependent drop down list for a High School. The User will select cell A1, Click on Hallway 3(for example), then the user will click on cell A1 again and then select the Room #, 325 (for example). The final result should be that cell A1 shows 325. I can create the first drop down list, but the second part is where I am having great trouble. I am using Excel 2010. Any help would be appreciated. Thanks

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  • Change Scan-to-PC list names on Brother MFC-8890DW Printer

    - by dralezero
    I have two Brother MFC-8890DW. When scanning over the network, it shows a list of PCs (on the scanner display) to save to that have the software/drivers installed. Each PC is listed as the name of the employee for that computer. I have setup a third MFC-8890DW and installed on these computers. The list, however, is the computer name. Somehow it is possible to customize the name. Brother support did not know. I couldn't find anything in manuals. I thought I remember setting up those names before.

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  • List processes with their launching command line

    - by rkolm_kds
    I'm looking for a Windows feature or third-party tool that can produce a list of active processes (as in the task manager) with the command line used to start each process. e.g. if I launch "php.exe -q script.php" in a command line, during the execution of my process, I'd like to see this command in the list and not only "php.exe" Tasklist, process explorer, taskinfo... can't give this information and/or make it available in a text format. Do you know if such tools/features exist? Thanks

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  • online to do list manager with subtasks

    - by alex
    I'm looking for an online task list tool, what I absolutely need is the infinite number of subtask levels, because that's how my mind works. I don't need collaboration. There are a lot of great to do list sites out there, but for some reason most of them have only one subtask level or no subtasks at all. I know about todoist, but its interface doesn't work for me. There must be many more, I guess. Links to desktop tools with the feature are also appreciated as long as they are cross-platform.

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  • Search desktop files using a list of keywords stored in a text file

    - by Tod1d
    I have a list of 1285 keywords (database object names) that I have compiled into a TXT file; one keyword per line. I would like to search a directory of files (most have a .aspx or .cs extension) using this list of keywords. My main goal is find out which of the 1285 database objects are being referenced in these files. Can anyone recommend a tool that could accomplish this? Otherwise, I will just create my own. Thanks.

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  • Find words from a list within a website

    - by Senoculus
    Summary: I need to find out if any items in my list occur in a website. I could do it manually with ctrl+f, but it would take a long time. Description I have a text file with key words in this format: word1 word4 word12 word24 ... I need to search text in a table on a website (in Internet Explorer) with this format: RandomWord version 1.3 ... word1 version 1.3 ... word2 version 2.6 ... word5 version 1.1 ... randomword version 9.0 ... word12 version 1.0 ... ... ... ... If the above data was what I had, it would be nice to end up with this list: word1 word12

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  • How to reference or vlookup a list of values based on a comma separated list of column references within a cell in excel?

    - by glallen
    I want to do a vlookup (or similar) against a column which is a list of values. This works fine for looking up a value from a single row, but I want to be able to look up multiple rows, sum the results, and divide by the number of rows referenced. For example: A B C D E F G [----given values----------------] [Work/Auth] [sum(vlookup(each(G),table,5)) /count(G)] [given vals] 1 Item Authorized OnHand Working Operational% DependencyOR% Dependencies 2 A 1 1 1 1 .55 B 3 B 10 5 5 .50 .55 C,D 4 C 100 75 50 .50 .60 D 5 D 10 10 6 .60 1 I want to be able to show an Operational Rate, and an operational rate of the systems each system depends on (F). In order to get a value for F, I want to sum over each value in column-E that was referenced by a dependency in column-G then divide by the number of dependencies in G. Column-G can have varying lengths, and will be a comma separated list of values from column-A. Is there any way to do this in excel?

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  • C#/.NET Little Wonders: Skip() and Take()

    - by James Michael Hare
    Once again, in this series of posts I look at the parts of the .NET Framework that may seem trivial, but can help improve your code by making it easier to write and maintain. The index of all my past little wonders posts can be found here. I’ve covered many valuable methods from System.Linq class library before, so you already know it’s packed with extension-method goodness.  Today I’d like to cover two small families I’ve neglected to mention before: Skip() and Take().  While these methods seem so simple, they are an easy way to create sub-sequences for IEnumerable<T>, much the way GetRange() creates sub-lists for List<T>. Skip() and SkipWhile() The Skip() family of methods is used to ignore items in a sequence until either a certain number are passed, or until a certain condition becomes false.  This makes the methods great for starting a sequence at a point possibly other than the first item of the original sequence.   The Skip() family of methods contains the following methods (shown below in extension method syntax): Skip(int count) Ignores the specified number of items and returns a sequence starting at the item after the last skipped item (if any).  SkipWhile(Func<T, bool> predicate) Ignores items as long as the predicate returns true and returns a sequence starting with the first item to invalidate the predicate (if any).  SkipWhile(Func<T, int, bool> predicate) Same as above, but passes not only the item itself to the predicate, but also the index of the item.  For example: 1: var list = new[] { 3.14, 2.72, 42.0, 9.9, 13.0, 101.0 }; 2:  3: // sequence contains { 2.72, 42.0, 9.9, 13.0, 101.0 } 4: var afterSecond = list.Skip(1); 5: Console.WriteLine(string.Join(", ", afterSecond)); 6:  7: // sequence contains { 42.0, 9.9, 13.0, 101.0 } 8: var afterFirstDoubleDigit = list.SkipWhile(v => v < 10.0); 9: Console.WriteLine(string.Join(", ", afterFirstDoubleDigit)); Note that the SkipWhile() stops skipping at the first item that returns false and returns from there to the rest of the sequence, even if further items in that sequence also would satisfy the predicate (otherwise, you’d probably be using Where() instead, of course). If you do use the form of SkipWhile() which also passes an index into the predicate, then you should keep in mind that this is the index of the item in the sequence you are calling SkipWhile() from, not the index in the original collection.  That is, consider the following: 1: var list = new[] { 1.0, 1.1, 1.2, 2.2, 2.3, 2.4 }; 2:  3: // Get all items < 10, then 4: var whatAmI = list 5: .Skip(2) 6: .SkipWhile((i, x) => i > x); For this example the result above is 2.4, and not 1.2, 2.2, 2.3, 2.4 as some might expect.  The key is knowing what the index is that’s passed to the predicate in SkipWhile().  In the code above, because Skip(2) skips 1.0 and 1.1, the sequence passed to SkipWhile() begins at 1.2 and thus it considers the “index” of 1.2 to be 0 and not 2.  This same logic applies when using any of the extension methods that have an overload that allows you to pass an index into the delegate, such as SkipWhile(), TakeWhile(), Select(), Where(), etc.  It should also be noted, that it’s fine to Skip() more items than exist in the sequence (an empty sequence is the result), or even to Skip(0) which results in the full sequence.  So why would it ever be useful to return Skip(0) deliberately?  One reason might be to return a List<T> as an immutable sequence.  Consider this class: 1: public class MyClass 2: { 3: private List<int> _myList = new List<int>(); 4:  5: // works on surface, but one can cast back to List<int> and mutate the original... 6: public IEnumerable<int> OneWay 7: { 8: get { return _myList; } 9: } 10:  11: // works, but still has Add() etc which throw at runtime if accidentally called 12: public ReadOnlyCollection<int> AnotherWay 13: { 14: get { return new ReadOnlyCollection<int>(_myList); } 15: } 16:  17: // immutable, can't be cast back to List<int>, doesn't have methods that throw at runtime 18: public IEnumerable<int> YetAnotherWay 19: { 20: get { return _myList.Skip(0); } 21: } 22: } This code snippet shows three (among many) ways to return an internal sequence in varying levels of immutability.  Obviously if you just try to return as IEnumerable<T> without doing anything more, there’s always the danger the caller could cast back to List<T> and mutate your internal structure.  You could also return a ReadOnlyCollection<T>, but this still has the mutating methods, they just throw at runtime when called instead of giving compiler errors.  Finally, you can return the internal list as a sequence using Skip(0) which skips no items and just runs an iterator through the list.  The result is an iterator, which cannot be cast back to List<T>.  Of course, there’s many ways to do this (including just cloning the list, etc.) but the point is it illustrates a potential use of using an explicit Skip(0). Take() and TakeWhile() The Take() and TakeWhile() methods can be though of as somewhat of the inverse of Skip() and SkipWhile().  That is, while Skip() ignores the first X items and returns the rest, Take() returns a sequence of the first X items and ignores the rest.  Since they are somewhat of an inverse of each other, it makes sense that their calling signatures are identical (beyond the method name obviously): Take(int count) Returns a sequence containing up to the specified number of items. Anything after the count is ignored. TakeWhile(Func<T, bool> predicate) Returns a sequence containing items as long as the predicate returns true.  Anything from the point the predicate returns false and beyond is ignored. TakeWhile(Func<T, int, bool> predicate) Same as above, but passes not only the item itself to the predicate, but also the index of the item. So, for example, we could do the following: 1: var list = new[] { 1.0, 1.1, 1.2, 2.2, 2.3, 2.4 }; 2:  3: // sequence contains 1.0 and 1.1 4: var firstTwo = list.Take(2); 5:  6: // sequence contains 1.0, 1.1, 1.2 7: var underTwo = list.TakeWhile(i => i < 2.0); The same considerations for SkipWhile() with index apply to TakeWhile() with index, of course.  Using Skip() and Take() for sub-sequences A few weeks back, I talked about The List<T> Range Methods and showed how they could be used to get a sub-list of a List<T>.  This works well if you’re dealing with List<T>, or don’t mind converting to List<T>.  But if you have a simple IEnumerable<T> sequence and want to get a sub-sequence, you can also use Skip() and Take() to much the same effect: 1: var list = new List<double> { 1.0, 1.1, 1.2, 2.2, 2.3, 2.4 }; 2:  3: // results in List<T> containing { 1.2, 2.2, 2.3 } 4: var subList = list.GetRange(2, 3); 5:  6: // results in sequence containing { 1.2, 2.2, 2.3 } 7: var subSequence = list.Skip(2).Take(3); I say “much the same effect” because there are some differences.  First of all GetRange() will throw if the starting index or the count are greater than the number of items in the list, but Skip() and Take() do not.  Also GetRange() is a method off of List<T>, thus it can use direct indexing to get to the items much more efficiently, whereas Skip() and Take() operate on sequences and may actually have to walk through the items they skip to create the resulting sequence.  So each has their pros and cons.  My general rule of thumb is if I’m already working with a List<T> I’ll use GetRange(), but for any plain IEnumerable<T> sequence I’ll tend to prefer Skip() and Take() instead. Summary The Skip() and Take() families of LINQ extension methods are handy for producing sub-sequences from any IEnumerable<T> sequence.  Skip() will ignore the specified number of items and return the rest of the sequence, whereas Take() will return the specified number of items and ignore the rest of the sequence.  Similarly, the SkipWhile() and TakeWhile() methods can be used to skip or take items, respectively, until a given predicate returns false.    Technorati Tags: C#, CSharp, .NET, LINQ, IEnumerable<T>, Skip, Take, SkipWhile, TakeWhile

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  • Get entities ids from two similar collections using one method

    - by Patryk Roszczyniala
    I've got two lists: List<Integer, ZooEntity> zoos; List<Integer, List<ZooEntity>> groupOfZoos; These operations will return collections of values: Collection<ZooEntity> cz = zoos.values(); Collection<List<ZooEntity>> czList = groupOfZoos.values(); What I want to achieve is to get list of all zoo ids. List<Integer> zooIds = cz ids + czList ids; Of course I can create two methods to do what I want: public List<Integer> getIdsFromFlatList(Collection<ZooEntity> list) { List<Integer> ids = new ArrayList<Integer>(); for (ZooEntity z : list) { ids.add(z.getId()); } return ids; } public List<Integer> getIdsFromNestedList(Collection<List<ZooEntity>> list) { List<Integer> ids = new ArrayList<Integer>(); for (List<ZooEntity> zList : list) { for (ZooEntity z : zList) { ids.add(z.getId()); } } return ids; } As you can see those two methods are very similar and here is my question: Is it good to create one method (for example using generics) which will get ids from those two lists (zoos and groupOfZoos). If yes how it should look like? If no what is the best solution? BTW. This is only the example. I've got very similar problem at job and I want to do it in preety way (I can't change enities, I can change only getIds...() methods).

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  • How to shuffle pairs

    - by Jessy
    How to shuffle the elements in the pairs? The program below, generate all possible pairs and later shuffle the pairs. e.g. possible pairs before shuffle is ab,ac,ae,af..etc shuffled to ac,ae,af,ab...etc How to make it not only shuffled in pairs but within the elements in the pair itself? e.g. instead of ab, ac, how can I make ba, ac ? String[] pictureFile = {"a.jpg","b.jpg","c.jpg","d.jpg","e.jpg","f.jpg","g.jpg"}; List <String> pic1= Arrays.asList(pictureFile); ... ListGenerator pic2= new ListGenerator(pic1); ArrayList<ArrayList<Integer>> pic2= new ArrayList<ArrayList<Integer>>(); public class ListGenerator { public ListGenerator(List<String> pic1) { int size = pic1.size(); // create a list of all possible combinations for(int i = 0 ; i < size ; i++) { for(int j = (i+1) ; j < size ; j++) { ArrayList<Integer> temp = new ArrayList<Integer>(); temp.add(i); temp.add(j); pic2.add(temp); } } Collections.shuffle(pic2); } //This method return the shuffled list public ArrayList<ArrayList<Integer>> getList() { return pic2; } }

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  • How to use a linkedList and multiple classes with my Java GUI

    - by Asj
    How should I use a linked list with my GUI program? The program is supposed to have blocks with textareas and dropdown menus. The number of blocks depends on the number of times the user presses a button. It's supposed to be possible to put blocks within blocks. I want to store the information created, using a linked list and then saving to a file. I'm thinking, for the sub blocks, there would be linked lists within the linked list. Should I use Java.util.LinkedList? How do I add the information? A Node class? Should that be in a separate file? I started to try sitting up a linked list, but it's getting me confused. I'm still unsure about how a person is supposed to make GUI's. I've only seen really simple GUI's. Can anyone tell me how I should arrange things? At the moment, I have three files, one for the main GUI window, one for the question blocks to be inserted within that, and one for some tools to use within those two files to make the code easier to understand. But, there seems to be something wrong with the question block file, because I've been making the background white for each JPanel, and there's a gray outline around the question blocks when I run the program. I probably shouldn't paste a ton of code here... These are my files: http://asj127.webs.com/BuildAssessmentWindow.java http://asj127.webs.com/QuestionBlock.java http://asj127.webs.com/JPanelTools.java

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  • Most efficient way to update attribute of one instance

    - by Begbie00
    Hi all - I'm creating an arbitrary number of instances (using for loops and ranges). At some event in the future, I need to change an attribute for only one of the instances. What's the best way to do this? Right now, I'm doing the following: 1) Manage the instances in a list. 2) Iterate through the list to find a key value. 3) Once I find the right object within the list (i.e. key value = value I'm looking for), change whatever attribute I need to change. for Instance within ListofInstances: if Instance.KeyValue == SearchValue: Instance.AttributeToChange = 10 This feels really inefficient: I'm basically iterating over the entire list of instances, even through I only need to change an attribute in one of them. Should I be storing the Instance references in a structure more suitable for random access (e.g. dictionary with KeyValue as the dictionary key?) Is a dictionary any more efficient in this case? Should I be using something else? Thanks, Mike

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  • why toString method does not work here??

    - by user329820
    Hi this is my whole class ,I have added number 2 to the doubly linked list and then I want it to be be print in the concole but it will show this "datastructureproject.Node@f62373" thanks! package datastructureproject; public class DoublyLinkedList { private Node head = new Node(0); private Node tail = new Node(0); private int length = 0; public DoublyLinkedList() { head.setPrev(null); head.setNext(tail); tail.setPrev(head); tail.setNext(null); } public void add(int index, int value) throws IndexOutOfBoundsException { Node cursor = get(index); Node temp = new Node(value); temp.setPrev(cursor); temp.setNext(cursor.getNext()); cursor.getNext().setPrev(temp); cursor.setNext(temp); length++; } private Node get(int index) throws IndexOutOfBoundsException { if (index < 0 || index > length) { throw new IndexOutOfBoundsException(); } else { Node cursor = head; for (int i = 0; i < index; i++) { cursor = cursor.getNext(); } return cursor; } } public long size() { return length; } public boolean isEmpty() { return length == 0; } @Override public String toString() { StringBuffer result = new StringBuffer(); result.append("(head) - "); Node temp = head; while (temp.getNext() != tail) { temp = temp.getNext(); result.append(temp.getValue() + " - "); } result.append("(tail)"); return result.toString(); } public static void main(String[] args){ DoublyLinkedList list = new DoublyLinkedList(); list.add(0,2 ); System.out.println(list.get(0).toString()); } }

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  • What is wrong with this append func in C

    - by LuckySlevin
    My Struct Definitions. typedef struct inner_list {char word[100]; inner_list*next;} inner_list; typedef struct outer_list { char word [100]; inner_list * head; outer_list * next; } outer_list; And The problem part: void append(outer_list **q,char num[100],inner_list *p) { outer_list *temp,*r; temp = *q; char *str; if(*q==NULL) { temp = (outer_list *)malloc(sizeof(outer_list)); strcpy(temp->word,num); temp->head = p; temp->next=NULL; *q=temp; } else { temp = *q; while(temp->next !=NULL) { temp=temp->next; } r = (outer_list *)malloc(sizeof(outer_list)); strcpy(r->word,num); temp->head = p; r->next=NULL; temp->next=r; } } I don't know what is i'm doing wrong in this append function i'm sending a char array and a linked list to be stored another linked list. But i can't store the linked list in another linked list. I couldn't figure out the problem. Any ideas?

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  • Why can't my vector access the variables in my nested structs?

    - by chucknorris
    #include<iostream> #include<vector> #include<string> #include<list> using namespace std; struct record{ int id; string fName; }; struct cells{ list<record> rec; }; vector<cells> hp; int main() { **hp.front().rec.front().fName = "jon"; return 0; } I have 2 structs. The first struct, struct record, is composed of 2 regular variables. In struct 2, I have a linked list of type "record", which includes all the variable listed in struct 1. Why is it that when ever I attempt to access a variable in the structs, using my vector, I get the error "linked list iterator not dereferencable?"

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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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  • Replacement for Vern Buerg's list.com in 64 bit Windows 7

    - by Kevin
    I would like to find a replacement for list.com, specifically the ability to accept piped input. For example: p4 sync -n | list which accepts the output of the perforce command and displays the results in the viewer/editor for manipulation or saving. I know that I would send the output to a file and then open the file in the viewer/editor but I use it for temporary results. List.com doesn't work on 64 bit Windows 7.

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  • MVC Dropdown List isn't binding to the model.

    - by Rod McLeay
    Hi, I am trying set up a simple dropdown list but I dont seem to be able to get it to bind to the Model. I am using Asp.Net MVC and nhibernate. My dropdown list is declared like so: <%= Html.DropDownListFor(model => model.Project, (IEnumerable<SelectListItem>)ViewData["Projects"], " -- Select -- ", new { name = "Project" })%> I set up the select list like so: ViewData["Projects"] = new SelectList(projectRepository.GetAll(), "EntityGUID", "Name", editEntity.Project); This seems to bind the select list to the Dropdown fine, but the SelectedValue is not set. it shows up as the default --- Select --- Also when I save this data, the dropdown does not bind to the model, I have to manually set the object like so to save it: entity.Project = projectRepository.GetById(new Guid(Request["Project"].ToString())); I believe I have take the correct messures to have this item bind directly to my model. Is there something I am missing here? Many thanks for your time, Rod

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  • C#: IEnumerable, GetEnumerator, a simple, simple example please!

    - by Andrew White
    Hi there, Trying to create an uebersimple class that implements get enumerator, but failing madly due to lack of simple / non-functioning examples out there. All I want to do is create a wrapper around a data structure (in this case a list, but I might need a dictionary later) and add some functions. public class Album { public readonly string Artist; public readonly string Title; public Album(string artist, string title) { Artist = artist; Title = title; } } public class AlbumList { private List<Album> Albums = new List<Album>; public Count { get { return Albums.Count; } } ..... //Somehow GetEnumerator here to return Album } Thanks!

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