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• PHP - Database schema: version control, branching, migrations.

  - by Billiam

  I'm trying to come up with (or find) a reusable system for database schema versioning in php projects. There are a number of Rails-style migration projects available for php. http://code.google.com/p/mysql-php-migrations/ is a good example. It uses timestamps for migration files, which helps with conflicts between branches. General problem with this kind of system: When development branch A is checked out, and you want to check out branch B instead, B may have new migration files. This is fine, migrating to newer content is straight forward. If branch A has newer migration files, you would need to migrate downwards to the nearest shared patch. If branch A and B have significantly different code bases, you may have to migrate down even further. This may mean: Check out B, determine shared patch number, check out A, migrate downwards to this patch. This must be done from A since the actual applied patches are not available in B. Then, checkout branch B, and migrate to newest B patch. Reverse process again when going from B to A. Proposed system: When migrating upwards, instead of just storing the patch version, serialize the whole patch in database for later use, though I'd probably only need the down() method. When changing branches, compare patches that have been run to patches that are available in the destination branch. Determine nearest shared patch (or oldest difference, maybe) between db table of run patches and patches in destination branch by ID or hash. Could also look for new or missing patches that are buried under a number of shared patches between the two branches. Automatically merge down to the nearest shared patch, using the db table stored down() methods, and then merge up to the branche's latest patch. My question is: Is this system too crazy and/or fraught with consequences to bother developing? My experience with database schema versioning is limited to PHP autopatch, which is an up()-only system requiring filenames with sequential IDs.

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• Advice on improving programming skills, learning capabilities?

  - by anonymous-coward1234

  Hi all, After 2,5 years of professional Java programing, I still have problems that make my job difficult and, more importantly - more times that I would like to admit - not enjoyable. I would like to ask for advice by more experienced people on ways that would help me overcome them. These are the problems I have: I do not absorb new knowledge easily. Even when I understand something, after a couple of days I easily forget even basic stuff. Other co-workers, even with the same working experience, when reading new technologies put things easily into "context", and are able to compare in "real time| similar technologies they already have used. I always try to address all the issues to whatever I am doing at one go, which results in me trying to resolve too many problems at the same time, losing completely control. I find it difficult to make my mind on a single problem that I should address first, and even when I do, and find myself throwing away code that I wrote because I started addressing the wrong issue first. As far as architecture and data modeling is concerned, I have difficulty making decisions on what objects must be created, with what hierarchy, interfaces, abstraction etc. I imagine that - to a certain degree - these things come with experience. But after 2,5 years of Java programming, I would expect myself to have come much farther that I have come, both in terms of absorption and experience. Is there a way to improve my learning speed? Any books, methods, advice is welcome.

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• What's it like being a financial programmer?

  - by Mike

  As a student who's done an internship at a Silicon Valley company(non-financial), I'm curious to know what it's like working for a financial company doing software development. I'd expect the hours to be longer, and the pay to be higher. Specifically, I have the following questions: What's the work/life balance really like? Are you expected to work 80 hours a week most weeks? For those who have worked in non-financial software engineering jobs, how does being a financial software engineer compare in terms of work/life balance? How much does it pay? I'm curious as to starting(i.e. just got a BS) pay, as well as "top out" pay. (I'd prefer concrete numbers - ballpark is fine). Also, bonuses would be useful information. What jobs do financial programmers typically have? Are most just general software engineers, or do people typically have very specialized(i.e. AI or systems) backgrounds? Also, do most programmers have PhDs? Are programmers typically required to be at work, or are financial companies generally flexible about letting programmers work from home? When at work, do programmers have to dress formally? What are the technology environments like? Are finance companies using state-of-the-art hardware and software, or are they generally more conservative in upgrading their equipment? What programming languages are typically used? If VBA(shudder) is used, is it a large part of a finance company's workflow? If you could turn back the clock, would you still be a financial programmer? I'm going to keep this post open a little bit longer to get some more responses.

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• Possible to Inspect Innards of Core C# Functionality

  - by Nick Babcock

  I was struck today, with the inclination to compare the innards of Buffer.BlockCopy and Array.CopyTo. I am curious to see if Array.CopyTo called Buffer.BlockCopy behind the scenes. There is no practical purpose behind this, I just want to further my understanding of the C# language and how it is implemented. Don't jump the gun and accuse me of micro-optimization, but you can accuse me of being curious! When I ran ILasm on mscorlib.dll I received this for Array.CopyTo .method public hidebysig newslot virtual final instance void CopyTo(class System.Array 'array', int32 index) cil managed { // Code size 0 (0x0) } // end of method Array::CopyTo and this for Buffer.BlockCopy .method public hidebysig static void BlockCopy(class System.Array src, int32 srcOffset, class System.Array dst, int32 dstOffset, int32 count) cil managed internalcall { .custom instance void System.Security.SecuritySafeCriticalAttribute::.ctor() = ( 01 00 00 00 ) } // end of method Buffer::BlockCopy Which, frankly, baffles me. I've never run ILasm on a dll/exe I didn't create. Does this mean that I won't be able to see how these functions are implemented? Searching around only revealed a stackoverflow question, which Marc Gravell said [Buffer.BlockCopy] is basically a wrapper over a raw mem-copy While insightful, it doesn't answer my question if Array.CopyTo calls Buffer.BlockCopy. I'm specifically interested in if I'm able to see how these two functions are implemented, and if I had future questions about the internals of C#, if it is possible for me to investigate it. Or am I out of luck?

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• php string versus boolean speed test

  - by ae

  I'm looking at trying to optimise a particular function in a php app and foolishly assumed that a boolean lookup in a 'if' statement would be quicker than a string compare. But to check it I put together a short test (see below). To my surprise, the string lookup was quicker. Is there anything wrong with my test (I'm wired on too much coffee so I'm suspicious of my own code)? If not, I would be interested in any comments people have around string versus boolean lookups in php. The result for the first test (boolean lookup) was 0.168 The result for the second test (string lookup) was 0.005 <?php $how_many = 1000000; $counter1 = 0; $counter2 = 0; $abc = array('boolean_lookup'=>TRUE, 'string_lookup'=>'something_else'); $start = microtime(); for($i = 0; $i < $how_many; $i++) { if($abc['boolean_lookup']) { $counter1++; } } echo ($start - microtime()); echo '<hr>'; $start = microtime(); for($i = 0; $i < $how_many; $i++) { if($abc['string_lookup'] == 'something_else') { $counter2++; } } echo ($start - microtime());

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• Creating a DataTable by filtering another DataTable

  - by Jeff Dege

  I'm working on a system that currently has a fairly complicated function that returns a DataTable, which it then binds to a GUI control on a ASP.NET WebForm. My problem is that I need to filter the data returned - some of the data that is being returned should not be displayed to the user. I'm aware of DataTable.select(), but that's not really what I need. First, it returns an array of DataRows, and I need a DataTable, so I can databind it to the GUI control. But more importantly, the filtering I need to do isn't something that can be easily put into a simple expression. I have an array of the elements which I do not want displayed, and I need to compare each element from the DataTable against that array. What I could do, of course, is to create a new DataTable, reading everything out of the original, adding to the new what is appropriate, then databinding the new to the GUI control. But that just seems wrong, somehow. In this case, the number of elements in the original DataTable aren't likely to be enough that copying them all in memory is going to cause too much trouble, but I'm wondering if there is another way. Does the .NET DataTable have functionality that would allow me to filter via a callback function?

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• CMBufferQueueCreate fail, required parameters?

  - by Agustin

  Reading the documentation about iOS SDK CMBufferQueueCreate, it says that getDuration and version are required, all the others callbacks can be NULL. but running the following code: CFAllocatorRef allocator; CMBufferCallbacks *callbacks; callbacks = malloc(sizeof(CMBufferCallbacks)); callbacks->version = 0; callbacks->getDuration = timeCallback; callbacks->refcon = NULL; callbacks->getDecodeTimeStamp = NULL; callbacks->getPresentationTimeStamp = NULL; callbacks->isDataReady = NULL; callbacks->compare = NULL; callbacks->dataBecameReadyNotification = NULL; CMItemCount capacity = 4; OSStatus s = CMBufferQueueCreate(allocator, capacity, callbacks, queue); NSLog(@"QUEUE: %x", queue); NSLog(@"STATUS: %i", s); with timeCallback: CMTime timeCallback(CMBufferRef buf, void *refcon){ return CMTimeMake(1, 1); } and queue is: CMBufferQueueRef* queue; queue creations fails (queue = 0) and returns a status of: kCMBufferQueueError_RequiredParameterMissing = -12761, The callbacks variable is correctly initialized, at least the debugger says so. Somebody have played arround with CMBufferQueue? google doesn't know about that! Thanks

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• Comparable and Comparator contract with regards to null

  - by polygenelubricants

  Comparable contract specifies that e.compareTo(null) must throw NullPointerException. From the API: Note that null is not an instance of any class, and e.compareTo(null) should throw a NullPointerException even though e.equals(null) returns false. On the other hand, Comparator API mentions nothing about what needs to happen when comparing null. Consider the following attempt of a generic method that takes a Comparable, and return a Comparator for it that puts null as the minimum element. static <T extends Comparable<? super T>> Comparator<T> nullComparableComparator() { return new Comparator<T>() { @Override public int compare(T el1, T el2) { return el1 == null ? -1 : el2 == null ? +1 : el1.compareTo(el2); } }; } This allows us to do the following: List<Integer> numbers = new ArrayList<Integer>( Arrays.asList(3, 2, 1, null, null, 0) ); Comparator<Integer> numbersComp = nullComparableComparator(); Collections.sort(numbers, numbersComp); System.out.println(numbers); // "[null, null, 0, 1, 2, 3]" List<String> names = new ArrayList<String>( Arrays.asList("Bob", null, "Alice", "Carol") ); Comparator<String> namesComp = nullComparableComparator(); Collections.sort(names, namesComp); System.out.println(names); // "[null, Alice, Bob, Carol]" So the questions are: Is this an acceptable use of a Comparator, or is it violating an unwritten rule regarding comparing null and throwing NullPointerException? Is it ever a good idea to even have to sort a List containing null elements, or is that a sure sign of a design error?

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• Problem with .Contains

  - by Rene

  Hello there, I have a little problem which i can't solve. I want to use an SQL-In-Statement in Linq. I've read in this Forum and in other Forums that I have to use the .Contains (with reverse-thinking-notation :-)). As input i have a List of Guids. I first copied them into an array and then did something like that : datatoget = (from p in objectContext.MyDataSet where ArrayToSearch.Contains(p.Subtable.Id.ToString()) select p).ToList(); datatoget is the result in which all records matching the Subtable.Id (which is a Guid) should be stored. Subtable is a Detail-Table from MyData, and the Id is a Guid-Type. I've tried several things (Convert Guid to String, and then using .Contains, etc), but I always get an Exception which says : 'Linq to Entities' doesn't recognize the Method 'Boolean Contains(System.Guid) and is not able to Translate this method into a memory expression. (Something like that, because I'm using the German Version of VS2008) I am using L2E with .NET 3.5 and am programming in C# with VS 2008. I've read several Examples, but it doesn't work. Is it perhaps because of using Guid's instead of strings ? I've also tried to write my own compare-function, but I don't know how to integrate it so that .NET calls my function for comparing.

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• Using Hidden Markov Model for designing AI mp3 player

  - by Casper Slynge

  Hey guys. Im working on an assignment, where I want to design an AI for a mp3 player. The AI must be trained and designed with the use of a HMM method. The mp3 player shall have the functionality of adapting to its user, by analyzing incoming biological sensor data, and from this data the mp3 player will choose a genre for the next song. Given in the assignment is 14 samples of data: One sample consist of Heart Rate, Respiration, Skin Conductivity, Activity and finally the output genre. Below is the 14 samples of data, just for you to get an impression of what im talking about. Sample HR RSP SC Activity Genre S1 Medium Low High Low Rock S2 High Low Medium High Rock S3 High High Medium Low Classic S4 High Medium Low Medium Classic S5 Medium Medium Low Low Classic S6 Medium Low High High Rock S7 Medium High Medium Low Classic S8 High Medium High Low Rock S9 High High Low Low Classic S10 Medium Medium Medium Low Classic S11 Medium Medium High High Rock S12 Low Medium Medium High Classic S13 Medium High Low Low Classic S14 High Low Medium High Rock My time of work regarding HMM is quite low, so my question to you is if I got the right angle on the assignment. I have three different states for each sensor: Low, Medium, High. Two observations/output symbols: Rock, Classic In my own opinion I see my start probabilities as the weightened factors for either a Low, Medium or High state in the Heart Rate. So the ideal solution for the AI is that it will learn these 14 sets of samples. And when a users sensor input is received, the AI will compare the combination of states for all four sensors, with the already memorized samples. If there exist a matching combination, the AI will choose the genre, and if not it will choose a genre according to the weightened transition probabilities, while simultaniously updating the transition probabilities with the new data. Is this a right approach to take, or am I missing something ? Is there another way to determine the output probability (read about Maximum likelihood estimation by EM, but dont understand the concept)? Best regards, Casper

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• SQL Server 2008: Comparing similar records - Need to still display an ID for a record when the JOIN has no matches

  - by aleppke

  I'm writing a SQL Server 2008 report that will compare genetic test results for animals. A genetic test consists of an animalId, a gene and a result. Not all animals will have the same genes tested but I need to be able to display the results side-by-side for a given set of animals and only include the genes that are present for at least one of the selected animals. My TestResult table has the following data in it: animalId gene result 1 a CC 1 b CT 1 d TT 2 a CT 2 b CT 2 c TT 3 a CT 3 b TT 3 c CC 3 d CC 3 e TT I need to generate a result set that looks like the following. Note that Animal 3 is not being displayed (user doesn't want to see its results) and neither are results for Gene "e" since neither Animal 1 nor Animal 2 have a result for that gene: SireID SireResult CalfID CalfResult Gene 1 CC 2 CT a 1 CT 2 CT b 1 NULL 2 TT c 1 TT 2 NULL d But I can only manage to get this: SireID SireResult CalfID CalfResult Gene 1 CC 2 CT a 1 CT 2 CT b NULL NULL 2 TT c 1 TT NULL NULL d This is the query I'm using. SELECT sire.animalId AS 'SireID' ,sire.result AS 'SireResult' ,calf.animalId AS 'CalfID' ,calf.result AS 'CalfResult' ,sire.gene AS 'Gene' FROM (SELECT s.animalId ,s.result ,m1.gene FROM (SELECT [animalId ] ,result ,gene FROM TestResult WHERE animalId IN (1)) s FULL JOIN (SELECT DISTINCT gene FROM TestResult WHERE animalId IN (1, 2)) m1 ON s.marker = m1.marker) sire FULL JOIN (SELECT c.animalId ,c.result ,m2.gene FROM (SELECT animalId ,result ,gene FROM TestResult WHERE animalId IN (2)) c FULL JOIN (SELECT DISTINCT gene FROM TestResult WHERE animalId IN (1, 2)) m2 ON c.gene = m2.gene) calf ON sire.gene = calf.gene How do I get the SireIDs and CalfIDs to display their values when they don't have a record associated with a particular Gene? I was thinking of using COALESCE but I can't figure out how to specify the correct animalId to pass in. Any help would be appreciated.

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• Threads, Sockets, and Designing Low-Latency, High Concurrency Servers

  - by lazyconfabulator

  I've been thinking a lot lately about low-latency, high concurrency servers. Specifically, http servers. http servers (fast ones, anyway) can serve thousands of users simultaneously, with very little latency. So how do they do it? As near as I can tell, they all use events. Cherokee and Lighttpd use libevent. Nginx uses it's own event library performing much the same function of libevent, that is, picking a platform optimal strategy for polling events (like kqueue on *bsd, epoll on linux, /dev/poll on Solaris, etc). They all also seem to employ a strategy of multiprocess or multithread once the connection is made - using worker threads to handle the more cpu intensive tasks while another thread continues to listen and handle connections (via events). This is the extent of my understanding and ability to grok the thousand line sources of these applications. What I really want are finer details about how this all works. In examples of using events I've seen (and written) the events are handling both input and output. To this end, do the workers employ some sort of input/output queue to the event handling thread? Or are these worker threads handling their own input and output? I imagine a fixed amount of worker threads are spawned, and connections are lined up and served on demand, but how does the event thread feed these connections to the workers? I've read about FIFO queues and circular buffers, but I've yet to see any implementations to work from. Are there any? Do any use compare-and-swap instructions to avoid locking or is locking less detrimental to event polling than I think? Or have I misread the design entirely? Ultimately, I'd like to take enough away to improve some of my own event-driven network services. Bonus points to anyone providing solid implementation details (especially for stuff like low-latency queues) in C, as that's the language my network services are written in.

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• Dojo Widgets not rendering when returned in response to XhrPost

  - by lazynerd

  I am trying to capture the selected item in a Dijit Tree widget to render remaining part of the web page. Here is the code that captures the selected item and sends it to Django backend: <div dojoType="dijit.Tree" id="leftTree" store="leftTreeStore" childrenAttr="folders" query="{type:'folder'}" label="Explorer"> <script type="dojo/method" event="onClick" args="item"> alert("Execute of node " + termStore.getLabel(item)); var xhrArgs = { url: "/load-the-center-part-of-page", handleAs: "text", postData: dojo.toJson(leftTreeStore.getLabel(item), true), load: function(data) { dojo.byId("centerPane").innerHTML = data; //window.location = data; }, error: function(error) { dojo.byId("centerPane").innerHTML = "<p>Error in loading...</p>"; } } dojo.byId("centerPane").innerHTML = "<p>Loading...</p>"; var deferred = dojo.xhrPost(xhrArgs); </script> </div> The remaining part of the page contains HTML code with dojo widgets. This is the code sent back as 'response' to the select item event. Here is a snippet: <div dojoType="dijit.layout.TabContainer" id="tabs" jsId="tabs"> <div dojoType="dijit.layout.BorderContainer" title="Dashboard"> <div dojoType="dijit.layout.ContentPane" region="bottom"> first tab </div> </div> <div dojoType="dijit.layout.BorderContainer" title="Compare"> <div dojoType="dijit.layout.ContentPane" region="bottom"> Second Tab </div> </div> </div> It renders this html 'response' but without the dojo widgets. Is handleAs: "text" in XhrPost the culprit here?

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• Textually diffing JSON

  - by Richard Levasseur

  As part of my release processes, I have to compare some JSON configuration data used by my application. As a first attempt, I just pretty-printed the JSON and diff'ed them (using kdiff3 or just diff). As that data has grown, however, kdiff3 confuses different parts in the output, making additions look like giant modifies, odd deletions, etc. It makes it really hard to figure out what is different. I've tried other diff tools, too (meld, kompare, diff, a few others), but they all have the same problem. Despite my best efforts, I can't seem to format the JSON in a way that the diff tools can understand. Example data: [ { "name": "date", "type": "date", "nullable": true, "state": "enabled" }, { "name": "owner", "type": "string", "nullable": false, "state": "enabled", } ...lots more... ] The above probably wouldn't cause the problem (the problem occurs when there begin to be hundreds of lines), but thats the gist of what is being compared. Thats just a sample; the full objects are 4-5 attributes, and some attributes have 4-5 attributes in them. The attribute names are pretty uniform, but their values pretty varied. In general, it seems like all the diff tools confuse the closing "}" with the next objects closing "}". I can't seem to break them of this habit. I've tried adding whitespace, changing indentation, and adding some "BEGIN" and "END" strings before and after the respective objects, but the tool still get confused.

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• Query MySQL data from Excel (or vice-versa)

  - by Charles

  I'm trying to automate a tedious problem. I get large Excel (.xls or .csv, whatever's more convenient) files with lists of people. I want to compare these against my MySQL database.* At the moment I'm exporting MySQL tables and reading them from an Excel spreadsheet. At that point it's not difficult to use =LOOKUP() and such commands to do the work I need, and of course the various text processing I need to do is easy enough to do in Excel. But I can't help but think that this is more work than it needs to be. Is there some way to get at the MySQL data directly from Excel? Alternately, is there a way I could access a reasonably large (~10k records) csv file in a sql script? This seems to be rather basic, but I haven't managed to make it work so far. I found an ODBC connection for MySQL but that doesn't seem to do what I need. In particular, I'm testing whether the name matches or whether any of four email addresses match. I also return information on what matched for the benefit of the next person to use the data, something like "Name 'Bob Smith' not found, but 'Robert Smith' matches on email address robert.smith@foo".

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• Binary search in a sorted (memory-mapped ?) file in Java

  - by sds

  I am struggling to port a Perl program to Java, and learning Java as I go. A central component of the original program is a Perl module that does string prefix lookups in a +500 GB sorted text file using binary search (essentially, "seek" to a byte offset in the middle of the file, backtrack to nearest newline, compare line prefix with the search string, "seek" to half/double that byte offset, repeat until found...) I have experimented with several database solutions but found that nothing beats this in sheer lookup speed with data sets of this size. Do you know of any existing Java library that implements such functionality? Failing that, could you point me to some idiomatic example code that does random access reads in text files? Alternatively, I am not familiar with the new (?) Java I/O libraries but would it be an option to memory-map the 500 GB text file (I'm on a 64-bit machine with memory to spare) and do binary search on the memory-mapped byte array? I would be very interested to hear any experiences you have to share about this and similar problems.

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• Synchronizing files between Linux servers, through FTP

  - by Daniel Magliola

  I have the following configuration of servers: 1 central linux server, a VPS 8 satellite linux servers, "crappy shared hostings" I have a bunch of files that I need to have in all servers. Right now i'm copying them everywhere manually, but I want to be able to copy them to the central server, and then have a scheduled process that runs every now and then and synchronizes them (only outwardly, no need to try to find "new" files in the satellite servers). There are a couple of catches though: I can't have any custom software in the satellite servers, or do strange command line things that'll auto connect to them and send the files directly. I know this is the way these kinds of things are normally done, but the satellite servers are crappy shared hosting ones where I have absolutely no control over anything. I need to send the files over FTP I also need to have, in my central server, a list of the files that are available in each of the satellite servers, to make sure they are ready before I send traffic to them. If I were to do this manually, the steps would be: get the list of files in a satellite server compare to my own, and send the files that are missing get the list of files again, and store it in my central database. I'd like to know what tools are out there that can alleviate as much of this as possible, first the syncing, and then the "getting the list of files available in the other server". I'm going to be doing everything from PHP, not sure if there are good tools to "use FTP from PHP", which i'm pretty sure i'll have to do for step 3 at least. Thanks in advance for any ideas! Daniel

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• How can I add a "Loading...Please wait..." feature?

  - by Rob

  I have a very simple table on my website, that displays different URL's. I have an input field where I can type in a URL and click 'Submit' to add additional URL's. However, I want to add an MD5 grabbing feature to this, using @md5_file(); to grab the MD5 of the URL and check to make sure it's the MD5 it should be, before adding it to the database. However it may take a few seconds for it to grab the MD5 and compare it, so I would like to add a little bit of text, like "Processing...Please wait..." while it does the comparing, and then once it's compared I want that text to go away. I've never done this before, or even though about doing it so I have no idea where to start. I'll go ahead and put javascript as a tag for this, since I'm guessing it would be done with javascript, but I really have no idea. I don't think it's possible with PHP, but again, I have no idea. Any suggestions?

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• Which is the best free ide/plugin for struts2?

  - by Shahensha

  Hello friends, I have just learnt struts 2 and now I have taken up a full fledged project in it. I learnt the basics of struts 2 in Netbeans with it's struts2 plugin. But I am not at all happy with it, as it is very basic and I end up doing most of the work. It is obviously better than plain-vanilla text editor, but still not at all near to what netbeans provides for springs and hibernate. I know because netbeans provides native support for springs and hibernate, it is meant to be better. I don't mind changing my IDE if i get better support for struts2! So my questions are Please list all the free IDEs where native support for struts2 is provided. And if possible please compare them. Please list all the plugins that are available for eclipse for struts2 development. I have heard there are better plugins in eclipse. Also, if there are better plugins in any other IDE (other than netbeans or eclipse of course), please list them giving links. Please give me some tips which I'll need before starting a full blown project in Struts2. I haven't worked on any project on Struts2. I have just finished reading Struts 2 in Action of Manning publications. Thanking you in advance! regards shahensha

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• T-SQL - Left Outer Joins - Fileters in the where clause versus the on clause.

  - by Greg Potter

  I am trying to compare two tables to find rows in each table that is not in the other. Table 1 has a groupby column to create 2 sets of data within table one. groupby number ----------- ----------- 1 1 1 2 2 1 2 2 2 4 Table 2 has only one column. number ----------- 1 3 4 So Table 1 has the values 1,2,4 in group 2 and Table 2 has the values 1,3,4. I expect the following result when joining for Group 2: `Table 1 LEFT OUTER Join Table 2` T1_Groupby T1_Number T2_Number ----------- ----------- ----------- 2 2 NULL `Table 2 LEFT OUTER Join Table 1` T1_Groupby T1_Number T2_Number ----------- ----------- ----------- NULL NULL 3 The only way I can get this to work is if I put a where clause for the first join: PRINT 'Table 1 LEFT OUTER Join Table 2, with WHERE clause' select table1.groupby as [T1_Groupby], table1.number as [T1_Number], table2.number as [T2_Number] from table1 LEFT OUTER join table2 --****************************** on table1.number = table2.number --****************************** WHERE table1.groupby = 2 AND table2.number IS NULL and a filter in the ON for the second: PRINT 'Table 2 LEFT OUTER Join Table 1, with ON clause' select table1.groupby as [T1_Groupby], table1.number as [T1_Number], table2.number as [T2_Number] from table2 LEFT OUTER join table1 --****************************** on table2.number = table1.number AND table1.groupby = 2 --****************************** WHERE table1.number IS NULL Can anyone come up with a way of not using the filter in the on clause but in the where clause? The context of this is I have a staging area in a database and I want to identify new records and records that have been deleted. The groupby field is the equivalent of a batchid for an extract and I am comparing the latest extract in a temp table to a the batch from yesterday stored in a partioneds table, which also has all the previously extracted batches as well. Code to create table 1 and 2: create table table1 (number int, groupby int) create table table2 (number int) insert into table1 (number, groupby) values (1, 1) insert into table1 (number, groupby) values (2, 1) insert into table1 (number, groupby) values (1, 2) insert into table2 (number) values (1) insert into table1 (number, groupby) values (2, 2) insert into table2 (number) values (3) insert into table1 (number, groupby) values (4, 2) insert into table2 (number) values (4)

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• Debug NAudio MP3 reading difference?

  - by Conrad Albrecht

  My code using NAudio to read one particular MP3 gets different results than several other commercial apps. Specifically: My NAudio-based code finds ~1.4 sec of silence at the beginning of this MP3 before "audible audio" (a drum pickup) starts, whereas other apps (Windows Media Player, RealPlayer, WavePad) show ~2.5 sec of silence before that same drum pickup. The particular MP3 is "Like A Rolling Stone" downloaded from Amazon.com. Tested several other MP3s and none show any similar difference between my code and other apps. Most MP3s don't start with such a long silence so I suspect that's the source of the difference. Debugging problems: I can't actually find a way to even prove that the other apps are right and NAudio/me is wrong, i.e. to compare block-by-block my code's results to a "known good reference implementation"; therefore I can't even precisely define the "error" I need to debug. Since my code reads thousands of samples during those 1.4 sec with no obvious errors, I can't think how to narrow down where/when in the input stream to look for a bug. The heart of the NAudio code is a P/Invoke call to acmStreamConvert(), which is a Windows "black box" call which I can't think how to error-check. Can anyone think of any tricks/techniques to debug this?

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• What's correct way to remove a boost::shared_ptr from a list?

  - by Catskul

  I have a std::list of boost::shared_ptr<T> and I want to remove an item from it but I only have a pointer of type T* which matches one of the items in the list. However I cant use myList.remove( tPtr ) I'm guessing because shared_ptr does not implement == for its template argument type. My immediate thought was to try myList.remove( shared_ptr<T>(tPtr) ) which is syntactically correct but it will crash from a double delete since the temporary shared_ptr has a separate use_count. std::list< boost::shared_ptr<T> > myList; T* tThisPtr = new T(); // This is wrong; only done for example code. // stand-in for actual code in T using // T's actual "this" pointer from within T { boost::shared_ptr<T> toAdd( tThisPtr ); // typically would be new T() myList.push_back( toAdd ); } { //T has pointer to myList so that upon a certain action, // it will remove itself romt the list //myList.remove( tThisPtr); //doesn't compile myList.remove( boost::shared_ptr<T>(tThisPtr) ); // compiles, but causes // double delete } The only options I see remaining are to use std::find with a custom compare, or to loop through the list brute force and find it myself, but it seems there should be a better way. Am I missing something obvious, or is this just too non-standard a use to be doing a remove the clean/normal way?

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• OpenCV shape matching

  - by MAckerman

  I'm new to OpenCV (am actually using Emgu CV C# wrapper) and am attempting to do some object detection. I'm attempting to determine if an object matches a predefined set of objects (that I will have to define). The background is well lit and does not move. My objects that I am starting with are bottles and cans. My current approach is: Do absDiff with a previously taken background image to separate the background. Then dilate 4x to make the lighter areas (in labels) shrink. Then I do a binary threshold to get a big blog, followed by finding contours in this image. I then take the largest contour and draw it, which becomes my shape to either save to the accepted set or compare with the accepted set. Currently I'm using cvMatchShapes, but the double return value seems to vary widely. I'm guessing it is because it doesn't take into account rotation. Is this approach a good one? It isn't working well for glass bottles since the edges are hard to find... I've read about haar classifiers, but thinking that might be overkill for my task.

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• Join + IEqualityComparer<T> and HashCode

  - by Jesus Rodriguez

  Im writing my own LINQ reference but Im getting troubles with some of the more complicated operators implementations. There is a Join implementation that takes a IEqualityComparer Im getting just crazy. Im trying to understand it first before I write (obviously) Image this two lists: List<string> initials = new List<string> {"A", "B", "C", "D", "E"}; List<string> words = new List<string> {"Ant", "Crawl", "Pig", "Boat", "Elephant", "Arc"}; Nothing weird here. I want to join both lists by the Initial, something like: Initial=A Word=Ant Initial=A Word=Arc Initial=B Word=Boat ... I need a comparator, I wrote this: public class InitialComparator : IEqualityComparer<string> { public bool Equals(string x, string y) { return x.StartsWith(y); } public int GetHashCode(string obj) { return obj[0].GetHashCode(); } } The Join itself: var blah = initials.Join(words, initial => initial, word => word, (initial, word) => new {Initial = initial, Word = word}, new InitialComparator()); It's the first time Im using HashCodes, after a good session of debugging I see that every word go to the comparator and look at its HashCode, if another word has the same HashCode it calls equals. Since I want to compare just the initial I though that I just need the first letter Hash (Am I wrong?) The thing is that this is not working correctly. Its says that "Ant" and "Arc" are equals, Ok, its comparing every word in the same list or not, But it adds only the last word it finds, in this case Arc, ignoring Ant and Ant is equals to "A" too... If I put "Ant" and "Ant" it add both. In short, What is the way of doing something like that? I know that Im doing something wrong. Thank you.

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• Java: Match tokens between two strings and return the number of matched tokens

  - by Cryssie

  Need some help to find the number of matched tokens between two strings. I have a list of string stored in ArrayList (example given below): Line 0 : WRB VBD NN VB IN CC RB VBP NNP Line 1 : WDT NNS VBD DT NN NNP NNP Line 2 : WRB MD PRP VB DT NN IN NNS POS JJ NNS Line 3 : WDT NN VBZ DT NN IN DT JJ NN IN DT NNP Line 4 : WP VBZ DT JJ NN IN NN Here, you can see each string consists of a bunch of tokens separated by spaces. So, there's three things I need to work with.. Compare the first token (WRB) in Line 0 to the tokens in Line 1 to see if they match. Move on to the next tokens in Line 0 until a match is found. If there's a match, mark the matched tokens in Line 1 so that it will not be matched again. Return the number of matched tokens between Line 0 and Line 1. Return the distance of the matched tokens. Example: token NN is found on position 3 on line 0 and position 5 on Line 1. Distance = |3-5| = 2 I've tried using split string and store it to String[] but String[] is fixed and doesn't allow shrinking or adding of new elements. Tried Pattern Matcher but with disasterous results. Tried a few other methods but there's some problems with my nested for loops..(will post part of my coding if it will help). Any advice or pointers on how to solve this problem this would be very much appreciated. Thank you very much.

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