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• Quickest algorithm for finding sets with high intersection

  - by conradlee

  I have a large number of user IDs (integers), potentially millions. These users all belong to various groups (sets of integers), such that there are on the order of 10 million groups. To simplify my example and get to the essence of it, let's assume that all groups contain 20 user IDs (i.e., all integer sets have a cardinality of 100). I want to find all pairs of integer sets that have an intersection of 15 or greater. Should I compare every pair of sets? (If I keep a data structure that maps userIDs to set membership, this would not be necessary.) What is the quickest way to do this? That is, what should my underlying data structure be for representing the integer sets? Sorted sets, unsorted---can hashing somehow help? And what algorithm should I use to compute set intersection)? I prefer answers that relate C/C++ (especially STL), but also any more general, algorithmic insights are welcome. Update Also, note that I will be running this in parallel in a shared memory environment, so ideas that cleanly extend to a parallel solution are preferred.

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• Radix Sort in Python [on hold]

  - by Steven Ramsey

  I could use some help. How would you write a program in python that implements a radix sort? Here is some info: A radix sort for base 10 integers is a based on sorting punch cards, but it turns out the sort is very ecient. The sort utilizes a main bin and 10 digit bins. Each bin acts like a queue and maintains its values in the order they arrive. The algorithm begins by placing each number in the main bin. Then it considers the ones digit for each value. The rst value is removed and placed in the digit bin corresponding to the ones digit. For example, 534 is placed in digit bin 4 and 662 is placed in the digit bin 2. Once all the values in the main bin are placed in the corresponding digit bin for ones, the values are collected from bin 0 to bin 9 (in that order) and placed back in the main bin. The process continues with the tens digit, the hundreds, and so on. After the last digit is processed, the main bin contains the values in order. Use randint, found in random, to create random integers from 1 to 100000. Use a list comphrension to create a list of varying sizes (10, 100, 1000, 10000, etc.). To use indexing to access the digits rst convert the integer to a string. For this sort to work, all numbers must have the same number of digits. To zero pad integers with leading zeros, use the string method str.zfill(). Once main bin is sorted, convert the strings back to integers. I'm not sure how to start this, Any help is appreciated. Thank you.

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• How do I add ROW_NUMBER to a LINQ query or Entity?

  - by Whozumommy

  I'm stumped by this easy data problem. I'm using the Entity framework and have a database of products. My results page returns a paginated list of these products. Right now my results are ordered by the number of sales of each product, so my code looks like this: return Products.OrderByDescending(u => u.Sales.Count()); This returns an IQueryable dataset of my entities, sorted by the number of sales. I want my results page to show the rank of each product (in the dataset). My results should look like this: Page #1 1. Bananas 2. Apples 3. Coffee Page #2 4. Cookies 5. Ice Cream 6. Lettuce I'm expecting that I just want to add a column in my results using the SQL ROW_NUMBER variable...but I don't know how to add this column to my results datatable. My resulting page does contain a foreach loop, but since I'm using a paginated set I'm guessing using that number to fake a ranking number would NOT be the best approach. So my question is, how do I add a ROW_NUMBER column to my query results in this case?

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• [UNIX] Sort lines of massive file by number of words on line (ideally in parallel)

  - by conradlee

  I am working on a community detection algorithm for analyzing social network data from Facebook. The first task, detecting all cliques in the graph, can be done efficiently in parallel, and leaves me with an output like this: 17118 17136 17392 17064 17093 17376 17118 17136 17356 17318 12345 17118 17136 17356 17283 17007 17059 17116 Each of these lines represents a unique clique (a collection of node ids), and I want to sort these lines in descending order by the number of ids per line. In the case of the example above, here's what the output should look like: 17118 17136 17356 17318 12345 17118 17136 17356 17283 17118 17136 17392 17064 17093 17376 17007 17059 17116 (Ties---i.e., lines with the same number of ids---can be sorted arbitrarily.) What is the most efficient way of sorting these lines. Keep the following points in mind: The file I want to sort could be larger than the physical memory of the machine Most of the machines that I'm running this on have several processors, so a parallel solution would be ideal An ideal solution would just be a shell script (probably using sort), but I'm open to simple solutions in python or perl (or any language, as long as it makes the task simple) This task is in some sense very easy---I'm not just looking for any old solution, but rather for a simple and above all efficient solution

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• Defining < for STL sort algorithm - operator overload, functor or standalone function?

  - by Andy

  I have a stl::list containing Widget class objects. They need to be sorted according to two members in the Widget class. For the sorting to work, I need to define a less-than comparator comparing two Widget objects. There seems to be a myriad of ways to do it. From what I can gather, one can either: a. Define a comparison operator overload in the class: bool Widget::operator< (const Widget &rhs) const b. Define a standalone function taking two Widgets: bool operator<(const Widget& lhs, const Widget& rhs); And then make the Widget class a friend of it: class Widget { // Various class definitions ... friend bool operator<(const Widget& lhs, const Widget& rhs); }; c. Define a functor and then include it as a parameter when calling the sort function: class Widget_Less : public binary_function<Widget, Widget, bool> { bool operator()(const Widget &lhs, const Widget& rhs) const; }; Does anybody know which method is better? In particular I am interested to know if I should do 1 or 2. I searched the book Effective STL by Scott Meyer but unfortunately it does not have anything to say about this. Thank you for your reply.

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• Model login constraints based on time

  - by DaDaDom

  Good morning, for an existing web application I need to implement "time based login constraints". It means that for each user, later maybe each group, I can define timeslots when they are (not) allowed to log in into the system. As all data for the application is stored in database tables, I need to somehow create a way to model this idea in that way. My first approach, I will try to explain it here: Create a tree of login constraints (called "timeslots") with the main "categories", like "workday", "weekend", "public holiday", etc. on the top level, which are in a "sorted" order (meaning "public holiday" has a higher priority than "weekday") for each top level node create subnodes, which have a finer timespan, like "monday", "tuesday", ... below that, create an "hour" level: 0, 1, 2, ..., 23. No further details are necessary. set every member to "allowed" by default For every member of the system create a 1:n relationship member:timeslots which defines constraints, e.g. a member A may have A:monday-forbidden and A:tuesday-forbidden Do a depth-first search at every login and check if the member has a constraint. Why a depth first search? Well, I thought that it may be that a member has the rules: A:monday->forbidden, A:monday-10->allowed, A:mondey-11->allowed So a login on monday at 12:30 would fail, but one at 10:30 succeed. For performance reasons I could break the relational database paradigm and set a flag for every entry in the member-to-timeslots-table which is set to true if the member has information set for "finer" timeslots, but that's a second step. Is this model in principle a good idea? Are there existing models? Thanks.

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• Why aren't my objects sorting with sortedArrayUsingDescriptors?

  - by clozach

  I expected the code below to return the objects in imageSet as a sorted array. Instead, there's no difference in the ordering before and after. NSSortDescriptor *descriptor = [[NSSortDescriptor alloc] initWithKey:@"imageID" ascending:YES]; NSSet *imageSet = collection.images; for (CBImage *image in imageSet) { NSLog(@"imageID in Set: %@",image.imageID); } NSArray *imageArray = [[imageSet allObjects] sortedArrayUsingDescriptors:(descriptor, nil)]; [descriptor release]; for (CBImage *image in imageArray) { NSLog(@"imageID in Array: %@",image.imageID); } Fwiw, CBImage is defined in my core data model. I don't know why sorting on managed objects would work any differently than on "regular" objects, but maybe it matters. As proof that @"imageID" should work as the key for the descriptor, here's what the two log loops above output for one of the sets I'm iterating through: 2010-05-05 00:49:52.876 Cover Browser[38678:207] imageID in Array: 360339 2010-05-05 00:49:52.876 Cover Browser[38678:207] imageID in Array: 360337 2010-05-05 00:49:52.877 Cover Browser[38678:207] imageID in Array: 360338 2010-05-05 00:49:52.878 Cover Browser[38678:207] imageID in Array: 360336 2010-05-05 00:49:52.879 Cover Browser[38678:207] imageID in Array: 360335 ... For extra credit, I'd love to get a general solution to troubleshooting NSSortDescriptor troubles (esp. if it also applies to troubleshooting NSPredicate). The functionality of these things seems totally opaque to me and consequently debugging takes forever.

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• How to store a list in a column of a database table.

  - by John Berryman

  Howdy! So, per Mehrdad's answer to a related question, I get it that a "proper" database table column doesn't store a list. Rather, you should create another table that effectively holds the elements of said list and then link to it directly or through a junction table. However, the type of list I want to create will be composed of unique items (unlike the linked question's fruit example). Furthermore, the items in my list are explicitly sorted - which means that if I stored the elements in another table, I'd have to sort them every time I accessed them. Finally, the list is basically atomic in that any time I wish to access the list, I will want to access the entire list rather than just a piece of it - so it seems silly to have to issue a database query to gather together pieces of the list. AKX's solution (linked above) is to serialize the list and store it in a binary column. But this also seems inconvenient because it means that I have to worry about serialization and deserialization. Is there any better solution? If there is no better solution, then why? It seems that this problem should come up from time to time. ... just a little more info to let you know where I'm coming from. As soon as I had just begun understanding SQL and databases in general, I was turned on to LINQ to SQL, and so now I'm a little spoiled because I expect to deal with my programming object model without having to think about how the objects are queried or stored in the database. Thanks All! John

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• Multi-level shop, xml or sql. best practice?

  - by danrichardson

  Hello, i have a general "best practice" question regarding building a multi-level shop, which i hope doesn't get marked down/deleted as i personally think it's quite a good "subjective" question. I am a developer in charge (in most part) of maintaining and evolving a cms system and associated front-end functionality. Over the past half year i have developed a multiple level shop system so that an infinite level of categories may exist down into a product level and all works fine. However over the last week or so i have questioned by own methods in front-end development and the best way to show the multi-level data structure. I currently use a sql server database (2000) and pull out all the shop levels and then process them into an enumerable typed list with child enumerable typed lists, so that all levels are sorted. This in my head seems quite process heavy, but we're not talking about thousands of rows, generally only 1-500 rows maybe. I have been toying with the idea recently of storing the structure in an XML document (as well as the database) and then sending last modified headers when serving/requesting the document for, which would then be processed as/when nessecary with an xsl(t) document - which would be processed server side. This is quite a handy, reusable method of storing the data but does it have more overheads in the fact im opening and closing files? And also the xml will require a bit of processing to pull out blocks of xml if for instance i wanted to show two level mid way through the tree for a side menu. I use the above method for sitemap purposes so there is currently already code i have built which does what i require, but unsure what the best process is to go about. Maybe a hybrid method which pulls out the data, sorts it and then makes an xml document/stream (XDocument/XmlDocument) for xsl processing is a good way? - This is the way i currently make the cms work for the shop. So really (and thanks for sticking with me on this), i am just wandering which methods other people use or recommend as being the best/most logical way of doing things. Thanks Dan

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• find and replace values in a flat-file using PHP

  - by peirix

  I'd think there was a question on this already, but I can't find one. Maybe the solution is too easy... Anyway, I have a flat-file and want to let the user change the values based on a name. I've already sorted out creating new name+value-pairs using the fopen('a') mode, using jQuery to send the AJAX call with newValue and newName. But say the content looks like this: host|http:www.stackoverflow.com folder|/questions/ folder2|/users/ And now I want to change the folder value. So I'll send in folder as oldName and /tags/ as newValue. What's the best way to overwrite the value? The order in the list doesn't matter, and the name will always be on the left, followed by a |(pipe), the value and then a new-line. My first thought was to read the list, store it in an array, search all the [0]'s for oldName, then change the [1] that belongs to it, and then write it back to a file. But I feel there is a better way around this? Any ideas? Maybe regex?

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• Can any linux API or tool watch for any change in any folder below e.g. /SharedRoot or do I have to

  - by Simon B.

  I have a folder with ~10 000 subfolders. Can any linux API or tool watch for any change in any folder below e.g. /SharedRoot or do I have to setup inotify for each folder? (i.e. I loose if I want to do this for 10k+ folders). I guess yes, since I've already seen examples of this inefficient method, for instance http://twistedmatrix.com/trac/browser/trunk/twisted/internet/inotify.py?rev=28866#L345 My problem: I need to keep folders time-sorted with most recently active "project" up top. When a file changes, each folder above that file should update its last-modified timestamp to match the file. Delays are ok. Opening a file (typically MS Excel) and closing again, its file date can jump up and then down again. For this reason I need to wait until after a file is closed, then queue the folder of that file for checking, and only a while later do I go and look for the newest file in its folder, since the filedate of the triggering file could already be back-dated to its original timestamp by Excel or similar programs. Also in case several files from same folder are used/created, it makes sense to buffer timestamping of that folders' parents to at least get a bunch of updates collapsed into one delayed update. I'm looking for a linux solution. I have some code that can be run on a windows server, most of the queing functionality is here: http://github.com/sesam/FolderdateFollowsFiles/blob/master/FolderdateFollowsFiles/Follower.vb Available API:s The relative of inotify on windows, ReadDirectoryChangesW, can watch a folder and its whole subtree; see bWatchSubtree on http://msdn.microsoft.com/en-us/library/aa365465(VS.85).aspx Samba? Patching samba source is a possibility, but perhaps there are already hooks available? Other possibilities, like client side (various windows versions) and spying on file activities in order to update folders recursively?

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• Confused about definition of a 'median' when constructing a kd-Tree

  - by user352636

  Hi there. Im trying to build a kd-tree for searching through a set of points, but am getting confused about the use of 'median' in the wikipedia article. For ease of use, the wikipedia article states the pseudo-code of kd-tree construction as: function kdtree (list of points pointList, int depth) { if pointList is empty return nil; else { // Select axis based on depth so that axis cycles through all valid values var int axis := depth mod k; // Sort point list and choose median as pivot element select median by axis from pointList; // Create node and construct subtrees var tree_node node; node.location := median; node.leftChild := kdtree(points in pointList before median, depth+1); node.rightChild := kdtree(points in pointList after median, depth+1); return node; } } I'm getting confused about the "select median..." line, simply because I'm not quite sure what is the 'right' way to apply a median here. As far as I know, the median of an odd-sized (sorted) list of numbers is the middle element (aka, for a list of 5 things, element number 3, or index 2 in a standard zero-based array), and the median of an even-sized array is the sum of the two 'middle' elements divided by two (aka, for a list of 6 things, the median is the sum of elements 3 and 4 - or 2 and 3, if zero-indexed - divided by 2.). However, surely that definition does not work here as we are working with a distinct set of points? How then does one choose the correct median for an even-sized list of numbers, especially for a length 2 list? I appreciate any and all help, thanks! -Stephen

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• Read text file into listbox collections

  - by Arcadian

  Hi, i'm new to C#. I need my program to show different parts of the data contained in a txt file into different listboxs (which are on different tabs of a form) so that the user can see the particular block of data they are interested in. the data contained in the txt file looks like this: G30:39:03:31 JG06 G32:56:36:10 JG04 G31:54:69:52 JG04 G36:32:53:11 JG05 G33:50:05:11 JG06 G39:28:81:21 JG01 G39:22:74:11 JG06 G39:51:44:21 JG03 G39:51:52:22 JG01 G39:51:73:21 JG01 G35:76:24:20 JG06 G35:76:55:11 JG01 G36:31:96:11 JG02 G36:31:96:23 JG02 G36:31:96:41 JG03 though much more of it :) The separate listboxes will contain only the lines who's first integer pair matches that listbox's name. For example, all the lines that start "G32" will be added to the G32 listbox. I think the code would start something like: private void ReadToBox() { FileInfo file = new FileInfo("Jumpgate List.JG"); StreamReader objRead = file.OpenText(); while (!objRead.EndOfStream) but i'm not sure where to start in terms of getting it sorted yet. Any help? There's some rep in it for you :D

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• Is the order of params important in NHibernate?

  - by Blake Blackwell

  If I have an int parameter followed by a string parameter in a sproc I get the following error: Input string was not in the correct format However, if I switch those parameters in the sproc than I get the result set I expect. Are params sorted by data type, or do I have to do anything special in my config file? I've included my code for reference: Config File <?xml version="1.0" encoding="utf-8" ?> <hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" assembly="NHibernateDemo" namespace="NHibernateDemo.Domain"> <class name="Blake_Test" table="Blake_Test"> <id name="TestId" column="TESTID"></id> <property name="TestName" column="TESTNAME" /> <loader query-ref="GetBlakeTest"/> </class> <sql-query name="GetBlakeTest" callable="true"> <return class="Blake_Test" /> call procedure AREA51.NHIBERNATE_TEST.GetBlakeTest(:int_TestId, :vch_TestName) </sql-query> </hibernate-mapping> Sproc Code: PROCEDURE GetBlakeTest ( ret_cursor OUT SYS_REFCURSOR, int_testid integer, vch_testname varchar2 ) AS BEGIN OPEN ret_cursor FOR SELECT TestId, TestName FROM blake_test WHERE testid = int_testid ORDER BY TestName DESC; END GetBlakeTest; END NHIBERNATE_TEST; Executing Code: IQuery query1 = session.GetNamedQuery( "GetBlakeTest" ); query1.SetParameter( "int_TestId", 1 ); query1.SetParameter( "vch_TestName", "TEST" ); IList<Blake_Test> mystuff = query1.List<Blake_Test>();

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• How to perform a binary search on IList<T>?

  - by Daniel Brückner

  Simple question - given an IList<T> how do you perform a binary search without writing the method yourself and without copying the data to a type with build-in binary search support. My current status is the following. List<T>.BinarySearch() is not a member of IList<T> There is no equivalent of the ArrayList.Adapter() method for List<T> IList<T> does not inherit from IList, hence using ArrayList.Adapter() is not possible I tend to believe that is not possible with build-in methods, but I cannot believe that such a basic method is missing from the BCL/FCL. If it is not possible, who can give the shortest, fastest, smartest, or most beatiful binary search implementation for IList<T>? UPDATE We all know that a list must be sorted before using binary search, hence you can assume that it is. But I assume (but did not verify) it is the same problem with sort - how do you sort IList<T>? CONCLUSION There seems to be no build-in binary search for IList<T>. One can use First() and OrderBy() LINQ methods to search and sort, but it will likly have a performance hit. Implementing it yourself (as an extension method) seems the best you can do.

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• Objective-C Getter Memory Management

  - by Marian André

  I'm fairly new to Objective-C and am not sure how to correctly deal with memory management in the following scenario: I have a Core Data Entity with a to-many relationship for the key "children". In order to access the children as an array, sorted by the column "position", I wrote the model class this way: @interface AbstractItem : NSManagedObject { NSArray * arrangedChildren; } @property (nonatomic, retain) NSSet * children; @property (nonatomic, retain) NSNumber * position; @property (nonatomic, retain) NSArray * arrangedChildren; @end @implementation AbstractItem @dynamic children; @dynamic position; @synthesize arrangedChildren; - (NSArray*)arrangedChildren { NSArray* unarrangedChildren = [[self.children allObjects] retain]; NSSortDescriptor* sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"position" ascending:YES]; [arrangedChildren release]; arrangedChildren = [unarrangedChildren sortedArrayUsingDescriptors:[NSArray arrayWithObject:sortDescriptor]]; [sortDescriptor release]; [unarrangedChildren release]; return [arrangedChildren retain]; } @end I'm not sure whether or not to retain unarrangedChildren and the returned arrangedChildren (first and last line of the arrangedChildren getter). Does the NSSet allObjects method already return a retained array? It's probably too late and I have a coffee overdose. I'd be really thankful if someone could point me in the right direction. I guess I'm missing vital parts of memory management knowledge and I will definitely look into it thoroughly.

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• Jquery set tr with empty td lower than with text in td

  - by PavelBY

  I have html, and jquery for sorting my table (also there is non-standart sorting (with multi-tbody)). My code could be found here: http://jsfiddle.net/GuRxj/ As you can see there, td with prices (on russian ????) are sorted ascending (but tech-as not!? why? (it a question too))... But as you see, i need to send this tr's with prices to top of this tbody (now there are in the bottom), while empty-price-tr send to bottom... How to do this? part of js: $('.prcol').click(function(e) { var $sort = this; var $table = $('#articles-table'); var $rows = $('tbody.analogs_art > tr',$table); $rows.sort(function(a, b){ var keyA = $('td:eq(3)',a).text(); var keyB = $('td:eq(3)',b).text(); if (keyA.length > 0 && keyB.length > 0) { if($($sort).hasClass('asc')){ console.log("bbb"); return (keyA > keyB) ? 1 : 0; } else { console.log(keyA+"-"+keyB); return (keyA > keyB) ? 1 : 0; } } }); $.each($rows, function(index, row){ //console.log(row); $table.append(row); //$("table.123").append(row); }); e.preventDefault(); });

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• how to display my list with n amount on each line in Python

  - by user1786698

  im trying to display my list with 7 states on each line here is what i have so far, but it displays as one long string of all the states with quotes around each state. I forgot to mention that this is for my CS class and we havent learned iter yet so we not allowed to use it. the only hint i was given was to to turn STATE_LIST into a string then use '\n' to break it up state = str(STATE_LIST) displaystates = Text(Point(WINDOW_WIDTH/2, WINDOW_HEIGHT/2), state.split('\n')) displaystates.draw(win) and STATE_LIST looks like this STATE_VOTES = { "AL" : 9, # Alabama "AK" : 3, # Alaska "AZ" : 11, # Arizona "AR" : 6, # Arkansas "CA" : 55, # California "CO" : 9, # Colorado "CT" : 7, # Connecticut "DE" : 3, # Delaware "DC" : 3, # Washington DC "FL" : 29, # Florida "GA" : 16, # Georgia "HI" : 4, # Hawaii "ID" : 4, # Idaho "IL" : 20, # Illinois "IN" : 11, # Indiana "IA" : 6, # Iowa "KS" : 6, # Kansas "KY" : 8, # Kentucky "LA" : 8, # Louisiana "ME" : 4, # Maine "MD" : 10, # Maryland "MA" : 11, # Massachusetts "MI" : 16, # Michigan "MN" : 10, # Minnesota "MS" : 6, # Mississippi "MO" : 10, # Missouri "MT" : 3, # Montana "NE" : 5, # Nebraska "NV" : 6, # Nevada "NH" : 4, # New Hampshire "NJ" : 14, # New Jersey "NM" : 5, # New Mexico "NY" : 29, # New York "NC" : 15, # North Carolina "ND" : 3, # North Dakota "OH" : 18, # Ohio "OK" : 7, # Oklahoma "OR" : 7, # Oregon "PA" : 20, # Pennsylvania "RI" : 4, # Rhode Island "SC" : 9, # South Carolina "SD" : 3, # South Dakota "TN" : 11, # Tennessee "TX" : 38, # Texas "UT" : 6, # Utah "VT" : 3, # Vermont "VA" : 13, # Virginia "WA" : 12, # Washington "WV" : 5, # West Virginia "WI" : 10, # Wisconsin "WY" : 3 # Wyoming } STATE_LIST = sorted(list(STATE_VOTES.keys())) I am trying to get it to look somewhat like this

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• Extending URIs with 2 queries (i.e. 'viewauthorbooks.php?authorid=4' AND 'orderby=returndate") Possi

  - by Jess

  I have a link in my system as displayed above; 'viewauthorbooks.php?authorid=4' which works fine and generates a page displaying the books only associated with the particular author. However I am implementing another feature where the user can sort the columns (return date, book name etc) and I am using the ORDER BY SQL clause. I have this also working as required for other pages, which do not already have another query in the URI. But for this particular page there is already a paramter returned in the URL, and I am having difficulty in extending it. When the user clicks on the a table column title I'm getting an error, and the original author ID is being lost!! This is the URI link I am trying to use: <th><a href="viewauthorbooks.php?authorid=<?php echo $row['authorid']?>&orderby=returndate">Return Date</a></th> This is so that the data can be sorted in order of Return Date. When I run this; the author ID gets lost for some reason, also I want to know if I am using correct layout to have 2 parameters run in the address? Thanks.

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• What is the most efficient/elegant way to parse a flat table into a tree?

  - by Tomalak

  Assume you have a flat table that stores an ordered tree hierarchy: Id Name ParentId Order 1 'Node 1' 0 10 2 'Node 1.1' 1 10 3 'Node 2' 0 20 4 'Node 1.1.1' 2 10 5 'Node 2.1' 3 10 6 'Node 1.2' 1 20 What minimalistic approach would you use to output that to HTML (or text, for that matter) as a correctly ordered, correctly intended tree? Assume further you only have basic data structures (arrays and hashmaps), no fancy objects with parent/children references, no ORM, no framework, just your two hands. The table is represented as a result set, which can be accessed randomly. Pseudo code or plain English is okay, this is purely a conceptional question. Bonus question: Is there a fundamentally better way to store a tree structure like this in a RDBMS? EDITS AND ADDITIONS To answer one commenter's (Mark Bessey's) question: A root node is not necessary, because it is never going to be displayed anyway. ParentId = 0 is the convention to express "these are top level". The Order column defines how nodes with the same parent are going to be sorted. The "result set" I spoke of can be pictured as an array of hashmaps (to stay in that terminology). For my example was meant to be already there. Some answers go the extra mile and construct it first, but thats okay. The tree can be arbitrarily deep. Each node can have N children. I did not exactly have a "millions of entries" tree in mind, though. Don't mistake my choice of node naming ('Node 1.1.1') for something to rely on. The nodes could equally well be called 'Frank' or 'Bob', no naming structure is implied, this was merely to make it readable. I have posted my own solution so you guys can pull it to pieces.

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• Need guidelines for optimizing WebGL performance by minimizing shader changes

  - by brainjam

  I'm trying to get an idea of the practicality of WebGL for rendering large architectural interior scenes, consisting of 100K's of triangles. These triangles are distributed over many objects, and there are many materials in the scene. On the other hand, there are no moving parts. And the materials tend to be fairly simple, mostly based on texture maps. There is a lot of texture map sharing .. for example all the chairs in scene will share a common map. There is also some multitexturing - up to three textures overlaid in a material. I've been doing a little experimentation and reading, and gather that frequently switching materials during a rendering pass will slow things down. For example, a scene with 200K triangles will have significant performance differences, depending on whether there are 10 or 1000 objects, assuming that each time an object is displayed a new material is set up. So it seems that if performance is important the scene should be sorted by materials so as to minimize material switching. What I'm looking for is guidelines on how to think of the overhead of various state changes, and where do I get the biggest bang for the buck. For example, what are the relative performance costs of, say, gl.useProgram(), gl.uniformMatrix4fv(), gl.drawElements() should I try to write ubershaders to minimize shader switching? should I try to aggregate geometry to minimize the number of gl.drawElements() calls I realize that mileage may vary depending on browser, OS, and graphics hardware. And I'm also not looking for heroic measures. Just some guidelines from people who have already had some experience in making scenes fast. I'll add that while I've had some experience with fixed-pipeline OpenGL programming in the past, I'm rather new to the WebGL/OpenGL ES 2.0 way of doing things.

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• Select all points in a matrix within 30m of another point

  - by pinnacler

  So if you look at my other posts, it's no surprise I'm building a robot that can collect data in a forest, and stick it on a map. We have algorithms that can detect tree centers and trunk diameters and can stick them on a cartesian XY plane. We're planning to use certain 'key' trees as natural landmarks for localizing the robot, using triangulation and trilateration among other methods, but programming this and keeping data straight and efficient is getting difficult using just Matlab. Is there a technique for sub-setting an array or matrix of points? Say I have 1000 trees stored over 1km (1000m), is there a way to say, select only points within 30m radius of my current location and work only with those? I would just use a GIS, but I'm doing this in Matlab and I'm unaware of any GIS plugins for Matlab. I forgot to mention, this code is going online, meaning it's going on a robot for real-time execution. I don't know if, as the map grows to several miles, using a different data structure will help or if calculating every distance to a random point is what a spatial database is going to do anyway. I'm thinking of mirroring two arrays, one sorted by X and the other by Y. Then bubble sorting to determine the 30m range in that. I do the same for both arrays, X and Y, and then have a third cross link table that will select the individual values. But I don't know, what that's called, how to program that and I'm sure someone already has so I don't want to reinvent the wheel. Cartesian Plane GIS

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• Clean up domain list in Excel - regex / macros?

  - by Tim

  I have a huge spreadsheet of domains that I need to clean up as follows: Remove all http:// (simple replace all - "http://" with "") Remove any www. (simple replace all - "www." with "") Delete any sub-domains (delete the actual row completely, not just the subdomain from the url) Remove anything after the domain extension (i.e. website.com/blah/blahbah/ becomes just website.com (simple replace all - "/*" with "", then replace all "/" with "") So what I'm left with is just a spreadsheet of clean domains like "website.com". I think I've got 1, 2 and 4 sorted (as above), but I'm really struggling with 3. Any ideas? Can I do this with regexp / vba, and actually delete the row completely? Sample data: http://www.scholastic.com/kids/stacks/games/ http://imgworld.teamworkonline.com/ http://topfreegraphics.com/ http://www.workcircle.co.uk/ http://www.healthycanadians.gc.ca/index-eng.php http://gsociology.icaap.org/methods/soft.html Post 1, 2 and 4 would leave me with: scholastic.com imgworld.teamworkonline.com topfreegraphics.com workcircle.co.uk healthycanadians.gc.ca gsociology.icaap.org It's those pesky sub-domains I need to just delete completely, just delete the row. I've realised I can't just search for 2 x ".", because obviously plenty of domain extensions (i.e .co.uk) include that. Any help appreciated.

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• WPF - How to stop an ItemsControl psuedo-grid's columns from dancing/jumping around during layout

  - by Drew Noakes

  Several other questions on SO have come to the same conclusion I have -- using an ItemsControl with a DataTemplate for each item constructed to position items such that they resemble a grid is much simpler (especially to format) than using a ListView. The code resembles: <StackPanel Grid.IsSharedSizeScope="True"> <!-- Header --> <Grid> <Grid.ColumnDefinitions> <ColumnDefinition Width="Auto" SharedSizeGroup="Column1" /> <ColumnDefinition Width="Auto" SharedSizeGroup="Column2" /> </Grid.ColumnDefinitions> <TextBlock Grid.Column="0" Text="Column Header 1" /> <TextBlock Grid.Column="1" Text="Column Header 2" /> </Grid> <!-- Items --> <ItemsControl ItemsSource="{Binding Path=Values, Mode=OneWay}"> <ItemsControl.ItemTemplate> <DataTemplate> <Grid> <Grid.ColumnDefinitions> <ColumnDefinition Width="Auto" SharedSizeGroup="Column1" /> <ColumnDefinition Width="Auto" SharedSizeGroup="Column2" /> </Grid.ColumnDefinitions> <TextBlock Grid.Column="0" Text="{Binding ColumnProperty1}" /> <TextBlock Grid.Column="1" Text="{Binding ColumnProperty2}" /> </Grid> </DataTemplate> </ItemsControl.ItemTemplate> </ItemsControl> </StackPanel> The problem I'm seeing is that whenever I swap the object to which the ItemsSource is bound (it's an ObservableCollection that I replace the reference to, rather than clear and re-add), the entire 'grid' dances about for a few seconds. Presumably it is making a few layout passes to get all the Auto-width columns to match up. This is very distracting for my users and I'd like to get it sorted out. Has anyone else seen this?

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• Poor performance using RMI-proxies with Swing components

  - by Patrick

  I'm having huge performance issues when I add RMI proxy references to a Java Swing JList-component. I'm retrieving a list of user Profiles with RMI from a server. The retrieval itself takes just a second or so, so that's acceptable under the circumstances. However, when I try to add these proxies to a JList, with the help of a custom ListModel and a CellRenderer, it takes between 30-60 seconds to add about 180 objects. Since it is a list of users' names, it's preferrable to present them alphabetically. The biggest performance hit is when I sort the elements as they get added to the ListModel. Since the list will always be sorted, I opted to use the built-in Collections.binarySearch() to find the correct position for the next element to be added, and the comparator uses two methods that are defined by the Profile interface, namely getFirstName() and getLastName(). Is there any way to speed this process up, or am I simply implementing it the wrong way? Or is this a "feature" of RMI? I'd really love to be able to cache some of the data of the remote objects locally, to minimize the remote method calls.

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