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• Subset generation by rules

  - by Sazug

  Let's say that we have a 5000 users in database. User row has sex column, place where he/she was born column and status (married or not married) column. How to generate a random subset (let's say 100 users) that would satisfy these conditions: 40% should be males and 60% - females 50% should be born in USA, 20% born in UK, 20% born in Canada, 10% in Australia 70% should be married and 30% not. These conditions are independent, that is we cannot do like this: (0.4 * 0.5 * 0.7) * 100 = 14 users that are males, born in USA and married (0.4 * 0.5 * 0.3) * 100 = 6 users that are males, born in USA and not married. Is there an algorithm to this generation?

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• how to rearrange randomly and show all the 5 elements

  - by user295189

  how can I rearrange it randomly and NOT use shuffle function and still be able to randomly arrange all the elements $input = array("Neo", "Morpheus", "Trinity", "Cypher", "Tank"); $rand_keys = array_rand($input, 5); echo $input[$rand_keys[0]] . "\n"; echo $input[$rand_keys[1]] . "\n"; echo $input[$rand_keys[2]] . "\n"; echo $input[$rand_keys[3]] . "\n"; echo $input[$rand_keys[4]] . "\n"; so it shows random names everytime the function is ran. thanks

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• How to write this function as a pL/pgSQl function ?

  - by morpheous

  I am trying to implement some business logic in a PL/pgSQL function. I have hacked together some pseudo code that explains the type of business logic I want to include in the function. Note: This function returns a table, so I can use it in a query like: SELECT A.col1, B.col1 FROM (SELECT * from some_table_returning_func(1, 1, 2, 3)) as A, tbl2 as B; The pseudocode of the pl/PgSQL function is below: CREATE FUNCTION some_table_returning_func(uid int, type_id int, filter_type_id int, filter_id int) RETURNS TABLE AS $$ DECLARE where_clause text := 'tbl1.id = ' + uid; ret TABLE; BEGIN switch (filter_type_id) { case 1: switch (filter_id) { case 1: where_clause += ' AND tbl1.item_id = tbl2.id AND tbl2.type_id = filter_id'; break; //other cases follow ... } break; //other cases follow ... } // where clause has been built, now run query based on the type ret = SELECT [COL1, ... COLN] WHERE where_clause; IF (type_id <> 1) THEN return ret; ELSE return select * from another_table_returning_func(ret,123); ENDIF; END; $$ LANGUAGE plpgsql; I have the following questions: How can I write the function correctly to (i.e. EXECUTE the query with the generated WHERE clause, and to return a table How can I write a PL/pgSQL function that accepts a table and an integer and returns a table (another_table_returning_func) ?

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• What's the best way to offer javascript embed that won't slow a page down?

  - by Shpigford

  I have a chunk of javascript that users can copy and paste to put on their sites. I'm currently using the following code (ala WEDJE) that allows the rest of the page to load even if my script is slow or not responding. <script type="text/javascript"> var number = "987654321"; var key = "123abc"; (function(){ document.write('<div id="ttp"></div>'); s=document.createElement('script'); s.type="text/javascript"; s.src="http://example.com/javascripts/embed.js?" + Math.random(); setTimeout("document.getElementById('ttp').appendChild(s);",1); })() </script> But that method is a few years old and so I wasn't sure if there was a more efficient way of doing the same thing that others have come up with.

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• VS2005 project has dependency that is not built

  - by Eyal

  I have VS2005 solution that contains many projects and dependencies (some C++, some C#) - in the past it compiled successfully. when I rebuild all the solution it fails on a project claiming dll is missing (dll that was needed to built before according to dependency). the thing is that from time to time it fails on random project (not all the time the same project). I'm not sure it is meaningful but I see in output console Deleting intermediate and output files for project doesn't VS2005 go according to "Project Build Order" and ReBuild every project starting with its dependencies?

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• How secure are GUIDs in terms of predictability?

  - by ssg

  We're using .NET's Guid.NewGuid() to generate activation codes and API keys currently. I wonder if that poses a security problem since their algorithm is open. .NET Guid uses Win32 CoCreateGuid and I don't know it's internals (possibly MAC address + timestamp?). Can someone derive a second GUID out of the first one, or can he hit it with some smart guesses or is the randomness good enough so search space becomes too big? Generating random keys have the problem of collision, they need a double check before adding to a database. That's why we stuck with GUIDs but I'm unsure about their security for these purposes. Here are the 4 consecutive UUIDGEN outputs: c44dc549-5d92-4330-b451-b29a87848993 d56d4c8d-bfba-4b95-8332-e86d7f204c1c 63cdf958-9d5a-4b63-ae65-74e4237888ea 6fd09369-0fbd-456d-9c06-27fef4c8eca5 Here are 4 of them by Guid.NewGuid(): 0652b193-64c6-4c5e-ad06-9990e1ee3791 374b6313-34a0-4c28-b336-bb2ecd879d0f 3c5a345f-3865-4420-a62c-1cdfd2defed9 5b09d7dc-8546-4ccf-9c85-de0bf4f43bf0

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• Splitting a double vector into equal parts

  - by Cosmin

  Greetings, Any input on a way to divide a std::vector into two equal parts ? I need to find the smallest possible difference between |part1 - part2|. This is how I'm doing it now, but from what you can probably tell it will yield a non-optimal split in some cases. auto mid = std::find_if(prim, ultim, [&](double temp) -> bool { if(tempsum >= sum) return true; tempsum += temp; sum -= temp; return false; }); The vector is sorted, highest to lowest, values can indeed appear twice. I'm not expecting part1 and part2 to have the same numbers of elements, but sum(part1) should be as close as possible to sum(part2) For example if we would have { 2.4, 0.12, 1.26, 0.51, 0.70 }, the best split would be { 2.4, 0.12 } and { 1.26, 0.51, 0.70 }. If it helps, I'm trying to achieve the splitting algorithm for the Shannon Fano encoding. Any input is appreciated, thanks!

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• extension method phone format with country code as parameter

  - by frenchie

  Hi, I'm writing an extension method called ToPhoneFormat that formats a string of digits to phone numbers. Is it possible to add a parameter to the method that would enable me to call it like this: MyPhoneString.ToPhoneFormat(international code) That way, I could write MyPhoneString.ToPhoneFormat(1); to format a US phone number and MyPhoneString.ToPhoneFormat(33) to format a French phone number. I already wrote the method that does the formatting but I'm wondering how to build the constructor so that it works with a parameter when I'm calling it. Thanks.

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• Python and hebrew encoding/decoding error

  - by user340495

  Hey, I have sqlite database which I would like to insert values in Hebrew to I am keep getting the following error : UnicodeDecodeError: 'ascii' codec can't decode byte 0xd7 in position 0: ordinal not in range(128) my code is as following : runsql(u'INSERT into personal values(%(ID)d,%(name)s)' % {'ID':1,'name':fabricate_hebrew_name()}) def fabricate_hebrew_name(): hebrew_names = [u'????',u'???',u'???',u'???',u'????',u'???',u'????',u'???',u'????',u'?????',u'????',u'???',u'????'] return random.sample(names,1)[0].encode('utf-8') note: runsql executing the query on the sqlite database fabricate_hebrew_name() should return a string which could be used in my SQL query. any help is much appreciated.

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• When using a HiLo ID generation strategy, what types should be used to hold Ids?

  - by UpTheCreek

  I'm asking this from a c#/NHibnernate perspective, but it's generally applicable. The concern is that the HiLo strategy goes though id's pretty quickly, and for example a low record-count table (Such as Users) is sharing from the same set of id's as a high record-count table (Such as comments). So you can potentially get to high numbers quicker that with other strategies. So what do people recommend? Code side: int/uint/long/ulong? DBSide: int/bigint? My feeling is to go with longs and bigingts, but would like a sanity check :)

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• Approaches to replace cursor in pure AS3 / Flare project?

  - by peteorpeter

  Hi there good lookin, I've got a pure AS3 (no Flex) project that uses Flare to display and interact with a data visualization. I just implemented some panning behavior, so you can click and drag the visualization around, and now I'd like to give the user a visual indicator that this is possible, by switching the arrow cursor with a nice grabby-looking hand icon. The user can click and drag at any time except when the mouse is over a clickable node (at which time the cursor swaps to a pointer - this behavior is already in place). So... 1) Do I need to create my own custom bitmap/sprite or is there a palette of built-in cursors I can use? (I'm not using Flex.) 2) Is there a way to simply replace the default arrow with the pan cursor project-wide, or do I need to attach the swapping to mouse events on display objects? Can I use the stage object to make this behavior apply everywhere? 3) How do I perform the swap? Do I use the Cursor object directly or do I need to get involved with the CursorManager? Any guidance, pseudo-code, or words of wisdom is greatly appreciated!

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• How to format a string as a telephone number in C#

  - by Brian G

  I have a string "1112224444' it is a telephone number. I want to format as 111-222-4444 before I store it in a file. It is on a datarecord and I would prefer to be able to do this without assigning a new variable. I was thinking: String.Format("{0:###-###-####}", i["MyPhone"].ToString() ); but that does not seem to do the trick. ** UPDATE ** Ok. I went with this solution Convert.ToInt64(i["Customer Phone"]).ToString("###-###-#### ####") Now its gets messed up when the extension is less than 4 digits. It will fill in the numbers from the right. so 1112224444 333 becomes 11-221-244 3334 Any ideas?

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• Transform PDF to HTML, keep layout

  - by Tgr

  What methods are there to transform a PDF to HTML? It could be anything - online service, software, library. (Opensource preferred. In the last case, php or python would be preferred.) It has to keep the original layout (including page numbers, footnotes and such), keep the images (combining them to one single background image per page is acceptable) and keep the links. It should preferably output valid XHTML and clean up PDF features such as ligatures, but if there is some post-processing required, I can live with that. Something with a clean, relatively semantic HTML output would be great. The closest one I found was zamzar.org, but it choked on links. (Also, the HTML output is an ugly heap of absolutely positioned divs and needs post-processing because of encoding problems.)

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• What's the "Hello World!" of genetic algorithms good for?

  - by JohnIdol

  I found this very cool C++ sample , literally the "Hello World!" of genetic algorithms. I so decided to re-code the whole thing in C# and this is the result. Now I am asking myself: is there any practical application along the lines of generating a target string starting from a population of random strings? EDIT: my buddy on twitter just tweeted that "is useful for transcription type things such as translation. Does not have to be Monkey's". I wish I had a clue.

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• Avoiding a fork()/SIGCHLD race condition

  - by larry

  Please consider the following fork()/SIGCHLD pseudo-code. // main program excerpt for (;;) { if ( is_time_to_make_babies ) { pid = fork(); if (pid == -1) { /* fail */ } else if (pid == 0) { /* child stuff */ print "child started" exit } else { /* parent stuff */ print "parent forked new child ", pid children.add(pid); } } } // SIGCHLD handler sigchld_handler(signo) { while ( (pid = wait(status, WNOHANG)) > 0 ) { print "parent caught SIGCHLD from ", pid children.remove(pid); } } In the above example there's a race-condition. It's possible for "/* child stuff */" to finish before "/* parent stuff */" starts which can result in a child's pid being added to the list of children after it's exited, and never being removed. When the time comes for the app to close down, the parent will wait endlessly for the already-finished child to finish. One solution I can think of to counter this is to have two lists: started_children and finished_children. I'd add to started_children in the same place I'm adding to children now. But in the signal handler, instead of removing from children I'd add to finished_children. When the app closes down, the parent can simply wait until the difference between started_children and finished_children is zero. Another possible solution I can think of is using shared-memory, e.g. share the parent's list of children and let the children .add and .remove themselves? But I don't know too much about this. EDIT: Another possible solution, which was the first thing that came to mind, is to simply add a sleep(1) at the start of /* child stuff */ but that smells funny to me, which is why I left it out. I'm also not even sure it's a 100% fix. So, how would you correct this race-condition? And if there's a well-established recommended pattern for this, please let me know! Thanks.

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• Bitwise operators versus .NET abstractions for bit manipulation in C# prespective

  - by Leron

  I'm trying to get basic skills in working with bits using C#.NET. I posted an example yesterday with a simple problem that needs bit manipulation which led me to the fact that there are two main approaches - using bitwise operators or using .NET abstractions such as BitArray (Please let me know if there are more build-in tools for working with bits other than BitArray in .NET and how to find more info for them if there are?). I understand that bitwise operators work faster but using BitArray is something much more easier for me, but one thing I really try to avoid is learning bad practices. Even though my personal preferences are for the .NET abstraction(s) I want to know which i actually better to learn and use in a real program. Thinking about it I'm tempted to think that .NET abstractions are not that bad at, after all there must be reason to be there and maybe being a beginner it's more natural to learn the abstraction and later on improve my skills with low level operations, but this is just random thoughts.

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• Cocoa window position anomaly

  - by Marius

  Hello everyone, I have a weird problem with positioning a window on screen. I want to center the window on the screen, but i don't know how to do that. Here's what i've got. The window is created from nib by the main controller: IdentFormController *ftf = [[IdentFormController alloc] initWithWindowNibName:@"IdentForm"]; [[ftf window] makeKeyAndOrderFront:self]; Now the IdentFormController has awakeFromNib() method in which it tries to position the window. For the sake of simplicity i've just tried to do setFrameOrigin(NSMakePoint(0, 0)). What happens is as follows: The first time i create this window, everything works as expected. But if i create it again after releasing the previous, it starts appearing at random positions. Why does it do that?

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• search paths where one native library depends on another

  - by carneades

  I'm using JNA and Java but I think this question affects any native-to-nonnative bridge. I have a Java application which relies on lib1.dylib, and lib1.dylib relies on lib2.dylib. I want to put everything inside of my .app file on Mac. I can easily put lib1.dylib inside and set java.classpath (or NativeLibrary.addSearchPath()) to tell the JVM where to find lib1.dylib. The trouble is, I don't know how to communicate that lib1.dylib's dependencies are also in the location I provided. The result is that lib1 is loaded fine, but then lib2 can't be found since it's not in the operating system's library path. Anyone know how I can overcome this problem? I imagine it must come up plenty in big projects with large numbers of shared libraries.

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• How to check a radio button based upon the enum value

  - by user281180

  I have an enum. Based upon the value brought by model, I have to check radio button. How can I do that? <%=Html.RadioButton("Role", Role.Viewer)%><%= .Role.Viewer%> <%=Html.RadioButton("Role",.Role.Reporter)%><%= Role.Reporter%> <%=Html.RadioButton("Role",Role.User)%><%= Role.User%> My enum would be having the numbers 1 to 3 for e.g. How can I check the Role.Viewer if enum value selected is 1?

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• PHP float bug: PHP Hangs On Numeric Value

  - by jeroen

  I just read an interesting article about php hanging on certain float numbers, see The Register and Exploring Binary. I never explicitly use floats, I use number_format() to clean my input and display for example prices. Also, as far as I am aware, all input from for example forms are strings until I tell them otherwise so I am supposing that this problem does not affect me. Am I right, or do I need to check for example Wordpress and Squirrelmail installations on my server to see if they cast anything to float? Or better, grep all php files on my servers for float?

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• xpath help substring expression

  - by NA

  Hi i have a document from which i am trying to extract a date. But the problem is within the node along with the date their is some text too. Something like <div class="postHeader"> Posted on July 20, 2009 9:22 PM PDT </div> From this tag i just want the date item not the Posted on text. something like ./xhtml:div[@class = 'postHeader'] is getting everything. and to be precise, the document i have is basically a nodelist of this elements for eg i will get 10 nodes of these elements with different date values but to be worse the problem is sometime inside these tags some random other tags also pops us like anchors etc. Can i write a universal expath which will just get the date out of the div tag?

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• How can I help fellow students struggling in programming classes?

  - by David Barry

  I'm a computer science student finishing up my second semester of programming classes. I've enjoyed them quite a bit, and learned a lot, but it seems other students are struggling with the concepts and assignments more than I am. When an assignment is due, the inevitable group email comes out the day or two before with people needing some help either with a specific part of the problem, or sometimes people just seem to have a hard time knowing where to start. I'd really like to be able to help out, but I have a hard time thinking of the right way to give them help without giving them the answer. When I'm having trouble understanding a concept, a code snippet can go along way to helping me, but at the same time if it makes a lot of sense, it can be difficult to think of another way to go about it. Plus the Academic Integrity section of each assignment is always looming overhead warning against sharing code with others. I've tried using pseudo code to help give others an idea on program flow, leaving them to figure out how to implement certain aspects of it, but I didn't get too much feedback and don't know how much it actually helped them out, or if it just confused them further. So I'm basically looking to see if anyone has experience with this, or good ways that I can help out other students to nudge them in the right direction or help them think about the problem in the right way.

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• Speed up math code in C# by writing a C dll?

  - by Projectile Fish

  I have a very large nested for loop in which some multiplications and additions are performed on floating point numbers. for (int i = 0; i < length1; i++) { s = GetS(i); c = GetC(i); for(int j = 0; j < length2; j++) { double oldU = u[j]; u[j] = c * oldU + s * omega[i][j]; omega[i][j] = c * omega[i][j] - s * oldU; } } This loop is taking up the majority of my processing time and is a bottleneck. Would I be likely to see any speed improvements if I rewrite this loop in C and interface to it from C#?

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• Fastest way to zero out a 2d array in C?

  - by Eddy

  I want to repeatedly zero a large 2d array in C. This is what I do at the moment: for(j = 0; j < n; j++) { for(i = 0; i < n; i++) { array[i][j] = 0; } } I've tried using memset: memset(array, 0, sizeof(array)) But this only works for 1D arrays. When I printf the contents of the 2D array, the first row is zeroes, but then I got a load of random large numbers and it crashes.

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• problem with hierarchical clustering in Python

  - by user248237

  I am doing a hierarchical clustering a 2 dimensional matrix by correlation distance metric (i.e. 1 - Pearson correlation). My code is the following (the data is in a variable called "data"): from hcluster import * Y = pdist(data, 'correlation') cluster_type = 'average' Z = linkage(Y, cluster_type) dendrogram(Z) The error I get is: ValueError: Linkage 'Z' contains negative distances. What causes this error? The matrix "data" that I use is simply: [[ 156.651968 2345.168618] [ 158.089968 2032.840106] [ 207.996413 2786.779081] [ 151.885804 2286.70533 ] [ 154.33665 1967.74431 ] [ 150.060182 1931.991169] [ 133.800787 1978.539644] [ 112.743217 1478.903191] [ 125.388905 1422.3247 ]] I don't see how pdist could ever produce negative numbers when taking 1 - pearson correlation. Any ideas on this? thank you.

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