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• Fixing color in scatter plots in matplotlib

  - by ajhall

  Hi guys, I'm going to have to come back and add some examples if you need them, which you might. But, here's the skinny- I'm plotting scatter plots of lab data for my research. I need to be able to visually compare the scatter plots from one plot to the next, so I want to fix the color range on the scatter plots and add in a colorbar to each plot (which will be the same in each figure). Essentially, I'm fixing all aspects of the axes and colorspace etc. so that the plots are directly comparable by eye. For the life of me, I can't seem to get my scatter() command to properly set the color limits in the colorspace (default)... i.e., I figure out my total data's min and total data's max, then apply them to vmin, vmax, for the subset of data, and the color still does not come out properly in both plots. This must come up here and there, I can't be the only one that wants to compare various subsets of data amongst plots... so, how do you fix the colors so that each data keeps it's color between plots and doesn't get remapped to a different color due to the change in max/min of the subset -v- the whole set? I greatly appreciate all your thoughts!!! A mountain-dew and fiery-hot cheetos to all! -Allen

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• How to parse rss from a php page, using jQuery/jFeed?

  - by ricebowl

  I'm trying to fumble my way through parsing rss sensibly, using jQuery and jFeed. Because of the same origin policy I'm pulling the BBC's health news feed into a local page (http://www.davidrhysthomas.co.uk/play/proxy.php). Originally this was just the same proxy.php script as available in the jFeed download package, but due to my host's disabling allow_url_fopen() I've amended the php to the following: $url = "http://newsrss.bbc.co.uk/rss/newsonline_uk_edition/health/rss.xml"; $ch = curl_init(); curl_setopt($ch, CURLOPT_URL, $url); curl_setopt($ch, CURLOPT_HEADER, 0); curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1); $data = curl_exec($ch); echo "$data"; curl_close($ch); Which seems to generate the same/comparable contents as the original fopen on my local machine. Now that seems to be working, I'm looking at setting the jFeed script up to work with the page and, to my embarrassment, don't see how. I understand that, at the least, this should work: jQuery.getFeed({ url: 'http://www.davidrhysthomas.co.uk/play/proxy.php', success: function(feed) { alert(feed.title); } }); ...but, as I'm sure you anticipate, it doesn't. What non-output there is, is available for your perusal here: http://www.davidrhysthomas.co.uk/play/exampleTest.html. And I honestly don't have a clue what to do about it. If anyone could offer some pointers, tips, hints, or, at a pinch, a quick slap around the cheeks and a 'pull yourself together!' it'd be much appreciated... Thanks in advance =)

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• Anonymous union definition/declaration in a macro GNU vs VS2008

  - by Alan_m

  I am attempting to alter an IAR specific header file for a lpc2138 so it can compile with Visual Studio 2008 (to enable compatible unit testing). My problem involves converting register definitions to be hardware independent (not at a memory address) The "IAR-safe macro" is: #define __IO_REG32_BIT(NAME, ADDRESS, ATTRIBUTE, BIT_STRUCT) \ volatile __no_init ATTRIBUTE union \ { \ unsigned long NAME; \ BIT_STRUCT NAME ## _bit; \ } @ ADDRESS //declaration //(where __gpio0_bits is a structure that names //each of the 32 bits as P0_0, P0_1, etc) __IO_REG32_BIT(IO0PIN,0xE0028000,__READ_WRITE,__gpio0_bits); //usage IO0PIN = 0x0xAA55AA55; IO0PIN_bit.P0_5 = 0; This is my comparable "hardware independent" code: #define __IO_REG32_BIT(NAME, BIT_STRUCT)\ volatile union \ { \ unsigned long NAME; \ BIT_STRUCT NAME##_bit; \ } NAME; //declaration __IO_REG32_BIT(IO0PIN,__gpio0_bits); //usage IO0PIN.IO0PIN = 0xAA55AA55; IO0PIN.IO0PIN_bit.P0_5 = 1; This compiles and works but quite obviously my "hardware independent" usage does not match the "IAR-safe" usage. How do I alter my macro so I can use IO0PIN the same way I do in IAR? I feel this is a simple anonymous union matter but multiple attempts and variants have proven unsuccessful. Maybe the IAR GNU compiler supports anonymous unions and vs2008 does not. Thank you.

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• Extract attributes from NSManagedObject array.

  - by Pavel Peroutka

  NSFetchRequest *req = [NSFetchRequest init]; NSEntityDescription *descr = [NSEntityDescription entityForName:@"City" inManagedObjectContext:context]; [req setEntity:descr]; NSSortDescriptor *sort = [[NSSortDescriptor alloc] initWithKey:@"streetName" ascending:YES]; [req setSortDescriptors:[NSArray arrayWithObject:sort]]; [sort release]; //fetch NSError *error; NSArray *result = [context executeFetchRequest:req error:&error]; //extract names NSMutableArray *streets = [[NSMutableArray alloc] init]; for () { ??? = [array objectAtIndex:i]; [streets addObject:name]; } I expected Core Data to be little more intuitive. I am new in it and I could use some help. I fetched all objects(rows) from the entity (table) City. Now I have an array of objects. From the array I need to extract the attribute “streetName” to an array which will feed the picker. I figured I need to do it in the loop but I could not figure out the way to do it. Please help. I have a background with SQL but Core Data is still a big mystery to me. Is there any publication which would take a SQL statement and show comparable Core Data syntax? Thanks.

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• Any teams out there using TypeMock? Is it worth the hefty price tag?

  - by dferraro

  Hi, I hope this question is not 'controversial' - I'm just basically asking - has anyone here purchased TypeMock and been happy (or unhappy) with the results? We are a small dev shop of only 12 developers including the 2 dev managers. We've been using NMock so far but there are limitations. I have done research and started playing with TypeMock and I love it. It's super clean syntax and lets you basically mock everything, which is great for legacy code. The problem is - how do I justify to my boss spending 800-1200$ per license for an API which has 4-5 competitors that are completly free? 800-1200$ is how much Infragistrics or Telerik cost per license - and there sure as hell isn't 4-5 open source comparable UI frameworks... Which is why I find it a bit overpriced, albeit an awesome library... Any opinions / experiences are greatly appreciated. EDIT: after finding MOQ I thought I fell in love - until I found out that it's not fully supported in VB.NET because VB lacks lambda sub routines =(. Is anyone using MOQ for VB.NET? The problem is we are a mixed shop - we use C# for our CRM development and VB for everything else. Any guidence is greatly appreciated again

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• MKL Accelerated Math Libraries for Java...

  - by Kaopua

  I've looked at the related threads on StackOverflow and Googled with not much luck. I'm also very new to Java (I'm coming from a C# and .NET background) so please bear with me. There is so much available in the Java world it's pretty overwhelming. I'm starting on a new Java-on-Linux project that requires some heavy and highly repetitious numerical calculations (i.e. statistics, FFT, Linear Algebra, Matrices, etc.). So maximizing the performance of the mathematical operations is a requirement, as is ensuring the math is correct. So hence I have an interest in finding a Java library that perhaps leverages native acceleration such as MKL, and is proven (so commercial options are definitely a possibility here). In the .NET space there are highly optimized and MKL accelerated commercial Mathematical libraries such as Centerspace NMath and Extreme Optimization. Is there anything comparable in Java? Most of the math libraries I have found for Java either do not seem to be actively maintained (such as Colt) or do not appear to leverage MKL or other native acceleration (such as Apache Commons Math). I have considered trying to leverage MKL directly from Java myself (e.g. JNI), but me being new to Java (let alone interoperating between Java and native libraries) it seemed smarter finding a Java library that has already done this correctly, efficiently, and is proven. Again I apologize if I am mistaken or misguided (even in regarding any libraries I've mentioned) and my ignorance of the Java offerings. It's a whole new world for me coming from the heavily commercialized Microsoft stock so I could easily be mistaken on where to look and regarding the Java libraries I've mentioned. I would greatly appreciate any help or advice.

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• C# vs C - Big performance difference

  - by John

  I'm finding massive performance differences between similar code in C anc C#. The C code is: #include <stdio.h> #include <time.h> #include <math.h> main() { int i; double root; clock_t start = clock(); for (i = 0 ; i <= 100000000; i++){ root = sqrt(i); } printf("Time elapsed: %f\n", ((double)clock() - start) / CLOCKS_PER_SEC); } And the C# (console app) is: using System; using System.Collections.Generic; using System.Text; namespace ConsoleApplication2 { class Program { static void Main(string[] args) { DateTime startTime = DateTime.Now; double root; for (int i = 0; i <= 100000000; i++) { root = Math.Sqrt(i); } TimeSpan runTime = DateTime.Now - startTime; Console.WriteLine("Time elapsed: " + Convert.ToString(runTime.TotalMilliseconds/1000)); } } } With the above code, the C# completes in 0.328125 seconds (release version) and the C takes 11.14 seconds to run. The c is being compiled to a windows executable using mingw. I've always been under the assumption that C/C++ were faster or at least comparable to C#.net. What exactly is causing the C to run over 30 times slower? EDIT: It does appear that the C# optimizer was removing the root as it wasn't being used. I changed the root assignment to root += and printed out the total at the end. I've also compiled the C using cl.exe with the /O2 flag set for max speed. The results are now: 3.75 seconds for the C 2.61 seconds for the C# The C is still taking longer, but this is acceptable

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• Alternative to 'Dispatch for ASP' deployment plug-in?

  - by Django Reinhardt

  Hi there, we've recently stumbled across the excellent Dispatch for ASP deployment plug in. It looks great apart from one thing: It doesn't work with Visual Studio 2010, at least for us, anyway. (It's supposed to work fine.) (Yes, we've tried everything: We've managed to get Dispatch working for another FTP site, but not the main one we regularly deploy to. We have managed to connect to our main site through FileZilla FTP, so the site itself is configured correctly. All settings have been triple checked, but the software still throws up weird errors (always to do with its internal libraries).) So does anyone know of any other comparable FTP-based, deployment plug-ins for Visual Studio? Here's what Dispatch does (and so any suggested replacement must do): Monitor any altered files in the project. When a file is changed, it's added to a list of files to be deployed. To deploy these files to the live site, all we need to do is click "Upload" and the plugin will connect via FTP to our live site and upload all the files. We can filter out any filenames we don't want to be monitored/uploaded (e.g. .cs or web.config or /Images/, etc.) I think that's all the features that we need. Thanks for any suggestions!

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• What's the most efficient query?

  - by Aaron Carlino

  I have a table named Projects that has the following relationships: has many Contributions has many Payments In my result set, I need the following aggregate values: Number of unique contributors (DonorID on the Contribution table) Total contributed (SUM of Amount on Contribution table) Total paid (SUM of PaymentAmount on Payment table) Because there are so many aggregate functions and multiple joins, it gets messy do use standard aggregate functions the the GROUP BY clause. I also need the ability to sort and filter these fields. So I've come up with two options: Using subqueries: SELECT Project.ID AS PROJECT_ID, (SELECT SUM(PaymentAmount) FROM Payment WHERE ProjectID = PROJECT_ID) AS TotalPaidBack, (SELECT COUNT(DISTINCT DonorID) FROM Contribution WHERE RecipientID = PROJECT_ID) AS ContributorCount, (SELECT SUM(Amount) FROM Contribution WHERE RecipientID = PROJECT_ID) AS TotalReceived FROM Project; Using a temporary table: DROP TABLE IF EXISTS Project_Temp; CREATE TEMPORARY TABLE Project_Temp (project_id INT NOT NULL, total_payments INT, total_donors INT, total_received INT, PRIMARY KEY(project_id)) ENGINE=MEMORY; INSERT INTO Project_Temp (project_id,total_payments) SELECT `Project`.ID, IFNULL(SUM(PaymentAmount),0) FROM `Project` LEFT JOIN `Payment` ON ProjectID = `Project`.ID GROUP BY 1; INSERT INTO Project_Temp (project_id,total_donors,total_received) SELECT `Project`.ID, IFNULL(COUNT(DISTINCT DonorID),0), IFNULL(SUM(Amount),0) FROM `Project` LEFT JOIN `Contribution` ON RecipientID = `Project`.ID GROUP BY 1 ON DUPLICATE KEY UPDATE total_donors = VALUES(total_donors), total_received = VALUES(total_received); SELECT * FROM Project_Temp; Tests for both are pretty comparable, in the 0.7 - 0.8 seconds range with 1,000 rows. But I'm really concerned about scalability, and I don't want to have to re-engineer everything as my tables grow. What's the best approach?

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• Should I strip the XML declaration from suds output before parsing with lxml?

  - by mikl

  I’m trying to implement a SOAP webservice in Python 2.6 using the suds library. That is working well, but I’ve run into a problem when trying to parse the output with lxml. Suds returns a suds.sax.text.Text object with the reply from the SOAP service. The suds.sax.text.Text class is a subclass of the Python built-in Unicode class. In essence, it would be comparable with this Python statement: u'<?xml version="1.0" encoding="utf-8" ?><root><lotsofelements \></root>' Which is incongrous, since if the XML declaration is correct, the contents are UTF-8 encoded, and thus not a Python Unicode object (because those are stored in some internal encoding like UCS4). lxml will refuse to parse this, as documented, since there is no clear answer to what encoding it should be interpreted as. As I see it, there are two ways out of this bind: Strip the <?xml> declaration, including the encoding. Convert the output from Suds into a bytestring, using the specified encoding. Currently, the data I’m receiving from the webservice is within the ASCII-range, so either way will work, but both feels very much like ugly hacks to me, and I’m not quite sure what would happen, if I start to receive data that would need a wider range of Unicode characters. Any good ideas? I can’t imagine I’m the first one in this position…

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• Linq to Entities custom ordering via position mapping table

  - by Bigfellahull

  Hi, I have a news table and I would like to implement custom ordering. I have done this before via a positional mapping table which has newsIds and a position. I then LEFT OUTER JOIN the position table ON news.newsId = position.itemId with a select case statement CASE WHEN [position] IS NULL THEN 9999 ELSE [position] END and order by position asc, articleDate desc. Now I am trying to do the same with Linq to Entities. I have set up my tables with a PK, FK relationship so that my News object has an Entity Collection of positions. Now comes the bit I can't work out. How to implement the LEFT OUTER JOIN. I have so far: var query = SelectMany (n => n.Positions, (n, s) => new { n, s }) .OrderBy(x => x.s.position) .ThenByDescending(x => x.n.articleDate) .Select(x => x.n); This kinda works. However this uses a INNER JOIN so not what I am after. I had another idea: ret = ret.OrderBy(n => n.ShufflePositions.Select(s => s.position)); However I get the error DbSortClause expressions must have a type that is order comparable. I also tried ret = ret.GroupJoin(tse.ShufflePositions, n => n.id, s => s.itemId, (n, s) => new { n, s }) .OrderBy(x => x.s.Select(z => z.position)) .ThenByDescending(x => x.n.articleDate) .Select(x => x.n); but I get the same error! If anyone can help me out, it would be much appreciated!

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• Comparing two Objects which implement the same interface for equality / equivalence - Design help

  - by gav

  Hi All, I have an interface and two objects implementing that interface, massively simplied; public interface MyInterface { public int getId(); public int getName(); ... } public class A implements MyInterface { ... } public class B implements MyInterface { ... } We are migrating from using one implementation to the other but I need to check that the objects of type B that are generated are equivalent to those of type A. Specifically I mean that for all of the interface methods an object of Type A and Type B will return the same value (I'm just checking my code for generating this objects is correct). How would you go about this? Map<String, MyInterface> oldGeneratedObjects = getOldGeneratedObjects(); Map<String, MyInterface> newGeneratedObjects = getNewGeneratedObjects(); // TODO: Establish that for each Key the Values in the two maps return equivalent values. I'm looking for good coding practices and style here. I appreciate that I could just iterate through one key set pulling out both objects which should be equivalent and then just call all the methods and compare, I'm just thinking there may be a cleaner, more extensible way and I'm interested to learn what options there might be. Would it be appropriate / possible / advised to override equals or implement Comparable? Thanks in advance, Gavin

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• Why does instanceof seem to work in a static generic function sometimes?

  - by michael

  Greetings. This is my first post in this site. I thought that because of type erasure, one could not expect the following code to compile, and indeed, it did not compile on an earlier version of Eclipse. My understanding was that instanceof was a run-time operator and could not know about the generic type which would be, by run-time, compiled away: public static <E extends Comparable<? super E>> void SampleForQuestion(E e) { if ( !(e instanceof String) ) System.out.println("I am not a String"); else System.out.println("I am a String"); } However, I was surprised to see that one of your threads actually included some code like this in an answer, and my latest Eclipse (Galileo on Windows with JVM 1.6 rev 20) is perfectly happy with it -- and it works, too. (I did notice that someone said it worked on Eclipse but not in another IDE/JDK in that thread, but don't remember the specifics.) Can someone explain why it works, and more importantly, because I have to guide my students, whether it should be expected to work in the future. Thank you. (I hope the code formatting comes through correctly - it looks indented correctly from my perspective and there are no tabs.)

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• Are there any code critique sites or similar resources?

  - by Ukko

  I have noticed when people post example code illustrating some issue that they are having often they will gather a number of comments addressing the quality of the code they presented and not the actual problem asked. This is very helpful--if not well directed. Often, this is wasted effort since the asker is often not receptive and the code is often chopped down to something small to post leaving lots of rough edges. In the old days you would see people asking questions like this on comp.lang.lisp and other parts of the comp.lang hierarchy. But that bit of the net kind of sank into the sewers of neglect. Is there a comparable one-stop-shop today? I am partially asking for selfish reasons, I know how to write good idiomatic C, Lisp, O'Caml, and Java code. But I learned C++ pre-template and STL, those rusty skills are not really applicable to today's C++. I have picked up languages like Scala in a vacuum and get by, but am I really doing it correctly? There are so many ways you can abuse a language, I am currently working against a codebase of Fortran written in C, and I recognize and loathe the "that guy" who wrote it. I don't want to be someone else's "that guy" if I can help it. Just because it works does not mean that one did not totally miss the boat on how it should have been done. Do you seek out this type of critique? If so how, where and why? What types of benefits do you derive from it? How about abuse and trolls?

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• How to create custom query for CollectionOfElements

  - by Shervin

  Hi. I have problems creating a custom query. This is what entities: @Entity public class ApplicationProcess { @CollectionOfElements private Set<Template> defaultTemplates; //more fields } And Template.java @Embeddable @EqualsAndHashCode(exclude={"file", "selected", "used"}) public class Template implements Comparable<Template> { @Setter private ApplicationProcess applicationProcess; @Setter private Boolean used = Boolean.valueOf(false); public Template() { } @Parent public ApplicationProcess getApplicationProcess() { return applicationProcess; } @Column(nullable = false) @NotNull public String getName() { return name; } @Column(nullable = true) public Boolean isUsed() { return used; } public int compareTo(Template o) { return getName().compareTo(o.getName()); } } I want to create a update statement. I have tried these two: int v = entityManager.createQuery("update ApplicationProcess_defaultTemplates t set t.used = true " + "WHERE t.applicationProcess.id=:apId").setParameter("apId", ap.getId()) .executeUpdate(); ApplicationProcess_defaultTemplates is not mapped [update ApplicationProcess_defaultTemplates t set t.used = true WHERE t.applicationProcess.id=:apId] And I have tried int v = entityManager.createQuery("update Template t set t.used = true " + "WHERE t.applicationProcess.id=:apId").setParameter("apId", ap.getId()) .executeUpdate(); With the same error: Template is not mapped [update Template t set t.used = true WHERE t.applicationProcess.id=:apId] Any ideas? UPDATE I fixed it by creating native query int v = entityManager.createNativeQuery("update ApplicationProcess_defaultTemplates t set t.used=true where t.ApplicationProcess_id=:apId").setParameter("apId", ap.getId()).executeUpdate();

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• How to generate a monotone MART ROC in R?

  - by user1521587

  I am using R and applying MART (Alg. for multiple additive regression trees) on a training set to build prediction models. When I look at the ROC curve, it is not monotone. I would be grateful if someone can help me with how I should fix this. I am guessing the issue is that initially, MART generates n trees and if these trees are not the same for all the models I am building, the results will not be comparable. Here are the steps I take: 1) Fix the false-negative cost, c_fn. Let cost = c(0, 1, c_fn, 0). 2) use the following line to build the mart model: mart(x, y, lx, martmode='class', niter=2000, cost.mtx=cost) where x is the matrix of training set variables, y is the observation matrix, lx is the matrix which specifies which of the variables in x is numerical, which one categorical. 3) I predict the test set observations using the mart model found in step 2 using this line: y_pred = martpred(x_test, probs=T) 4) I compute the false-positive and false-negative errors as follows: t = 1/(1+c_fn) %threshold based on Bayes optimal rule where c_fp=1 and c_fn. p_0 = length(which(y_test==1))/dim(y_test)[1] p_01 = sum(1*(y_pred[,2]t & y_test==0))/dim(y_test)[1] p_11 = sum(1*(y_pred[,2]t & y_test==1))/dim(y_test)[1] p_fp = p_01/(1-p_0) p_tp = p_11/p_0 5) repeat step 1-4 for a new false-negative cost.

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• C++: defining maximum/minimum limits for a class

  - by Luis

  Basically what the title says... I have created a class that models time slots in a variable-granularity daily schedule (where for example the first time slot is 30 minutes, but the second time slot can be 40 minutes); the first available slot starts at (a value comparable to) 1. What I want to do now is to define somehow the maximum and minimum allowable values that this class takes and I have two practical questions in order to do so: 1.- does it make sense to define absolute minimum and maximum in such a way for a custom class? Or better, does it suffice that a value always compares as lower-than any other possible value of the type, given the class's defined relational operators, to be defined the min? (and analogusly for the max) 2.- assuming the previous question has an answer modeled after "yes" (or "yes but ..."), how do I define such max/min? I know that there is std::numeric_limits<> but from what I read it is intended for "numeric types". Do I interpret that as meaning "represented as a number" or can I make a broader assumption like "represented with numbers" or "having a correspondence to integers"? After all, it would make sense to define the minimum and maximum for a date class, and maybe for a dictionary class, but numeric_limits may not be intended for those uses (I don't have much experience with it). Plus, numeric_limits has a lot of extra members and information that I don't know what to make with. If I don't use numeric_limits, what other well-known / widely-used mechanism does C++ offer to indicate the available range of values for a class?

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• MySQL: SELECT highest column value when WHERE finds similar entries

  - by Ike

  My question is comparable to this one, but not quite the same. I have a database with a huge amount of books, with different editions of some of the same book titles. I'm looking for an SQL statement giving me the highest edition number of each of the titles I'm selecting with a WHERE clause (to find specific book series). Here's what the table looks like: |id|title |edition|year| |--|-------------------------|-------|----| |01|Serie One Title One |1 |2007| |02|Serie One Title One |2 |2008| |03|Serie One Title One |3 |2009| |04|Serie One Title Two |1 |2001| |05|Serie One Title Three |1 |2008| |06|Serie One Title Three |2 |2009| |07|Serie One Title Three |3 |2010| |08|Serie One Title Three |4 |2011| |--|-------------------------|-------|----| The result I'm looking for is this: |id|title |edition|year| |--|-------------------------|-------|----| |03|Serie One Title One |3 |2009| |04|Serie One Title Two |1 |2001| |08|Serie One Title Three |4 |2011| |--|-------------------------|-------|----| The closest I got was using this statement: select id, title, max(edition), max(year) from books where title like "serie one%" group by name; but it returns the highest edition and year and includes the first id it finds: |--|-----------------------|-------|----| |01|Serie One Title One |3 |2009| |04|Serie One Title Two |1 |2001| |05|Serie One Title Three |4 |2011| |--|-----------------------|-------|----| This fancy join also comes close, but doesn't give the right result: select b.id, b.title, b.edition, b.year from books b inner join (select name, max(edition) as maxedition from books group by title) g on b.edition = g.maxedition where b.title like "serie one%" group by title; Using this I'm getting unique titles, but mostly old editions.

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• Bizzare Java invalid Assignment Operator Error

  - by Kay

  public class MaxHeap<T extends Comparable<T>> implements Heap<T>{ private T[] heap; private int lastIndex; private static final int defaultInitialCapacity = 25; public void add(T newItem) throws HeapException{ if (lastIndex < Max_Heap){ heap[lastIndex] = newItem; int place = lastIndex; int parent = (place – 1)/2; //ERROR HERE********** while ( (parent >=0) && (heap[place].compareTo(heap[parent])>0)){ T temp = heap[place]; heap[place] = heap[parent]; heap[parent] = temp; place = parent; parent = (place-1)/2; }else { throw new HeapException(“HeapException: Heap full”); } } } Eclipse complains that there is a: "Syntax error on token "Invalid Character", invalid AssignmentOperator" With the red line beneath the '(place-1)' There shouldn't be an error at all since it's just straight-forward arithmetic. Or is it not that simple?

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• .NET port with Java's Map, Set, HashMap

  - by Nikos Baxevanis

  I am porting Java code in .NET and I am stuck in the following lines that (behave unexpectedly in .NET). Java: Map<Set<State>, Set<State>> sets = new HashMap<Set<State>, Set<State>>(); Set<State> p = new HashSet<State>(); if (!sets.containsKey(p)) { ... } The equivalent .NET code could possibly be: IDictionary<HashSet<State>, HashSet<State>> sets = new Dictionary<HashSet<State>, HashSet<State>>(); HashSet<State> p = new HashSet<State>(); if (!sets.containsKey(p)) { /* (Add to a list). Always get here in .NET (??) */ } However the code comparison fails, the program think that "sets" never contain Key "p" and eventually results in OutOfMemoryException. Perhaps I am missing something, object equality and identity might be different between Java and .NET. I tried implementing IComparable and IEquatable in class State but the results were the same. Edit: What the code does is: If the sets does not contain key "p" (which is a HashSet) it is going to add "p" at the end of a LinkedList. The State class (Java) is a simple class defined as: public class State implements Comparable<State> { boolean accept; Set<Transition> transitions; int number; int id; static int next_id; public State() { resetTransitions(); id = next_id++; } // ... public int compareTo(State s) { return s.id - id; } public boolean equals(Object obj) { return super.equals(obj); } public int hashCode() { return super.hashCode(); }

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• Abstract away a compound identity value for use in business logic?

  - by John K

  While separating business logic and data access logic into two different assemblies, I want to abstract away the concept of identity so that the business logic deals with one consistent identity without having to understand its actual representation in the data source. I've been calling this a compound identity abstraction. Data sources in this project are swappable and various and the business logic shouldn't care which data source is currently in use. The identity is the toughest part because its implementation can change per kind of data source, whereas other fields like name, address, etc are consistently scalar values. What I'm searching for is a good way to abstract the concept of identity, whether it be an existing library, a software pattern or just a solid good idea of some kind is provided. The proposed compound identity value would have to be comparable and usable in the business logic and passed back to the data source to specify records, entities and/or documents to affect, so the data source must be able to parse back out the details of its own compound ids. Data Source Examples: This serves to provide an idea of what I mean by various data sources having different identity implementations. A relational data source might express a piece of content with an integer identifier plus a language specific code. For example. content_id language Other Columns expressing details of content 1 en_us 1 fr_ca The identity of the first record in the above example is: 1 + en_us However when a NoSQL data source is substituted, it might somehow represent each piece of content with a GUID string 936DA01F-9ABD-4d9d-80C7-02AF85C822A8 plus language code of a different standardization, And a third kind of data source might use just a simple scalar value. So on and so forth, you get the idea.

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• How is this function being made use of?

  - by Kay

  Hello all, I am just studying a few classes given to me by my lecturer and I can't understand how the function heapRebuild is being made used of! It doesn't change any global variables and it doesn't print out anything ad it doesn't return anything - so should this even work? It shouldn't, should it? If you were told to make use of heapRebuild to make a new function removeMac would you edit heapRebuild? public class MaxHeap<T extends Comparable<T>> implements Heap<T>{ private T[] heap; private int lastIndex; public T removeMax(){ T rootItem = heap[0]; heap[0] = heap[lastIndex-1]; lastIndex--; heapRebuild(heap, 0, lastIndex); return rootItem; } protected void heapRebuild(T[ ] items, int root, int size){ int child = 2*root+1; if( child < size){ int rightChild = child+1; if ((rightChild < size) && (items[rightChild].compareTo(items[child]) > 0)){ child = rightChild; } if (items[root].compareTo(items[child]) < 0){ T temp = items[root]; items[root] = items[child]; items[child] = temp; heapRebuild(items, child, size);} } } }

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• C++0x Smart Pointer Comparisons: Inconsistent, what's the rationale?

  - by GManNickG

  In C++0x (n3126), smart pointers can be compared, both relationally and for equality. However, the way this is done seems inconsistent to me. For example, shared_ptr defines operator< be equivalent to: template <typename T, typename U> bool operator<(const shared_ptr<T>& a, const shared_ptr<T>& b) { return std::less<void*>()(a.get(), b.get()); } Using std::less provides total ordering with respect to pointer values, unlike a vanilla relational pointer comparison, which is unspecified. However, unique_ptr defines the same operator as: template <typename T1, typename D1, typename T2, typename D2> bool operator<(const unique_ptr<T1, D1>& a, const unique_ptr<T2, D2>& b) { return a.get() < b.get(); } It also defined the other relational operators in similar fashion. Why the change in method and "completeness"? That is, why does shared_ptr use std::less while unique_ptr uses the built-in operator<? And why doesn't shared_ptr also provide the other relational operators, like unique_ptr? I can understand the rationale behind either choice: with respect to method: it represents a pointer so just use the built-in pointer operators, versus it needs to be usable within an associative container so provide total ordering (like a vanilla pointer would get with the default std::less predicate template argument) with respect to completeness: it represents a pointer so provide all the same comparisons as a pointer, versus it is a class type and only needs to be less-than comparable to be used in an associative container, so only provide that requirement But I don't see why the choice changes depending on the smart pointer type. What am I missing? Bonus/related: std::shared_ptr seems to have followed from boost::shared_ptr, and the latter omits the other relational operators "by design" (and so std::shared_ptr does too). Why is this?

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• find the difference between two very large list

  - by user157195

  I have two large list(could be a hundred million items), the source of each list can be either from a database table or a flat file. both lists are of comparable sizes, both unsorted. I need to find the difference between them. so I have 3 scenarios: 1. List1 is a database table(assume each row simply have one item(key) that is a string), List2 is a large file. 2. Both lists are from 2 db tables. 3. both lists are from two files. in case 2, I plan to use: select a.item from MyTable a where a.item not in (select b.item form MyTable b) this clearly is inefficient, is there a better way? Another approach is: I plan to sort each list, and then walk down both of them to find the diff. If the list is from a file, I have to read it into a db table first, then use db sorting to output the list. Is the run time complexity still O(nlogn) in db sorting? either approach is a pain and seems would be very slow when the list involved has hundreds of millions of items. any suggestions?

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• MD3200 - 3 to 4x less throughput than MD1220. Am I missing something here?

  - by Igor Polishchuk

  I have two R710 servers with similar configuration. One in my office has MD1220 attached. Another one in the datacenter of my hosting services vendor has MD3200. I'm getting significantly worse throughput from MD3200 at my vendors setup. I'm mostly interested in sequential writes, and I'm getting these results in bonnie++ and dd tests: Seq. writes on MD1220 in my office: 1.1 GB/s - bonnie++, 1.3GB/s - dd Seq. writes on MD3200 at my vendor's: 240MB/s - bonnie++, 310MB/s - dd Unfortunately, I could not test the exactly the same configurations, but the two I have should be comparable. If anything, my good performing environment is cheaper than the bad performing. I expect at least similar throughput from these two setups. My vendor cannot really help me. Hopefully, somebody more familiar with the DAS performance can look at it and tell if I'm missing something here and my expectations are too high. To summarize, the question here is it reasonable to expect about 100MB/s of sequential write throughput per each couple of drives in RAID10 on MD3200? Is there any trick to enable such performance in MD3200 with dual controller as opposed to simple MD1220 with a single H800 adapter? More details about the configurations: A good one in my office: Dell R710 2CPU X5650 @ 2.67GHz 12 cores 96GB DDR3, OS: RHEL 5.5, kernel 2.6.18-194.26.1.el5 x86_64 20x300GB 2.5" SAS 10K in a single RAID10 1MB chunk size on MD1220 + Dell H800 I/O controller with 1GB cache in the host Not so good one at my vendor's: Dell R710 2CPU L5520 @ 2.27GHz 8 cores 144GB DDR3, OS: RHEL 5.5, kernel 2.6.18-194.11.4.el5 x86_64 20x146GB 2.5" SAS 15K in a single RAID10 512KB chunk size, Dell MD3200, 2 I/O controllers in array with 1GB cache each Additional information. I've also ran the same tests on the same vendor's host, but the storage was: two raids of 14x146GB 15K RPM drives RAID 10, striped together on the OS level on MD3000+MD1000. The performance was about 25% worse than on MD3200 despite having more drives. When I ran similar tests on the internal storage of my vendor's host (2x146GB 15K RPM drives RAID1, Perc 6i) I've got about 128MB/s seq. writes. Just two internal drives gave me about a half of 20 drives' throughput on MD3200. The random I/O performance of the MD3200 setup is ok, it gives me at least 1300 IOPS. I'm mostly have problems with sequentioal I/O throughput. Thank you for looking into it. Regards Igor

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