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• Comparison of collection datatypes in C#

  - by Joel in Gö

  Does anyone know of a good overview of the different C# collection types? I am looking for something showing which basic operations such as Add, Remove, RemoveLast etc. are supported, and giving the relative performance. It would be particularly interesting for the various generic classes - and even better if it showed eg. if there is a difference in performance between a List<T> where T is a class and one where T is a struct. A start would be a nice cheat-sheet for the abstract data structures, comparing Linked Lists, Hash Tables etc. etc. Thanks!

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• How to cast an array to an array with another primitive type

  - by Martijn Courteaux

  Hi, Can someone complete the code on an easy way? float[] floats = {...}; // create an array // Now I want to create a new array of ints from the arrays floats int[] ints = ????; I know I can simply cast element by element to a new array. But is it possible on an easier way? Thanks

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• when is java faster than c++ (or when is JIT faster then precompiled)?

  - by kostja

  I have heard that under certain circumstances, Java programs or rather parts of java programs are able to be executed faster than the "same" code in C++ (or other precompiled code) due to JIT optimizations. This is due to the compiler being able to determine the scope of some variables, avoid some conditionals and pull similar tricks at runtime. Could you give an (or better - some) example, where this applies? And maybe outline the exact conditions under which the compiler is able to optimize the bytecode beyond what is possible with precompiled code? NOTE : This question is not about comparing Java to C++. Its about the possibilities of JIT compiling. Please no flaming. I am also not aware of any duplicates. Please point them out if you are.

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• JSON.Stringify data including boolean values

  - by ancdev

  What I'm trying to do is to pass JSON object to a WebAPI ajax call and mapped to a strongly typed object on the server side. String values are being posted perfectly however when it comes to boolean values, they are not being passed at all. Below is my code: var gsGasolineField = $('.gsGasoline').val(); blData = { Gasoline: gsGasolineField }; var json = JSON.stringify(blData); $.ajax({ type: "POST", url: url, data: json, contentType: "application/json", dataType: "json", statusCode: { 201 /*Created"*/: function (data) { $("#BusinessLayerDialog").dialog("close"); ClearForm("#BusinessLayerForm"); }, 400: /*Bad request - validation error*/ function (data) { $("#BusinessLayerForm").validate().form(); }, 500: function (data) { alert('err'); } }, beforeSend: setHeader }); Gasoline property is of type boolean on the server side.

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• ASP.NET (C#) jQuery JSON data problem

  - by oraclee

  My JSON Data {"menu": { "id": "file", "value": "File", "popup": { "menuitem": [ {"value": "New", "onclick": "CreateNewDoc()"}, {"value": "Open", "onclick": "OpenDoc()"}, {"value": "Close", "onclick": "CloseDoc()"} ] } }} jQuery code: $(document).ready(function() { $("#Button1").click(function() { var asd = "test"; $.get("CallBack.Aspx", { asd: asd }, function(data) { $.each(data, function() { }) }) }) }) I need menuitem in values how to make ? "menuitem": [ { "value": "New", "onclick": "CreateNewDoc()" } ]

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• Scalable Database Tagging Schema

  - by Longpoke

  EDIT: To people building tagging systems. Don't read this. It is not what you are looking for. I asked this when I wasn't aware that RDBMS all have their own optimization methods, just use a simple many to many scheme. I have a posting system that has millions of posts. Each post can have an infinite number of tags associated with it. Users can create tags which have notes, date created, owner, etc. A tag is almost like a post itself, because people can post notes about the tag. Each tag association has an owner and date, so we can see who added the tag and when. My question is how can I implement this? It has to be fast searching posts by tag, or tags by post. Also, users can add tags to posts by typing the name into a field, kind of like the google search bar, it has to fill in the rest of the tag name for you. I have 3 solutions at the moment, but not sure which is the best, or if there is a better way. Note that I'm not showing the layout of notes since it will be trivial once I get a proper solution for tags. Method 1. Linked list tagId in post points to a linked list in tag_assoc, the application must traverse the list until flink=0 post: id, content, ownerId, date, tagId, notesId tag_assoc: id, tagId, ownerId, flink tag: id, name, notesId Method 2. Denormalization tags is simply a VARCHAR or TEXT field containing a tab delimited array of tagId:ownerId. It cannot be a fixed size. post: id, content, ownerId, date, tags, notesId tag: id, name, notesId Method 3. Toxi (from: http://www.pui.ch/phred/archives/2005/04/tags-database-schemas.html, also same thing here: http://stackoverflow.com/questions/20856/how-do-you-recommend-implementing-tags-or-tagging) post: id, content, ownerId, date, notesId tag_assoc: ownerId, tagId, postId tag: id, name, notesId Method 3 raises the question, how fast will it be to iterate through every single row in tag_assoc? Methods 1 and 2 should be fast for returning tags by post, but for posts by tag, another lookup table must be made. The last thing I have to worry about is optimizing searching tags by name, I have not worked that out yet. I made an ASCII diagram here: http://pastebin.com/f1c4e0e53

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• What limits scaling in this simple OpenMP program?

  - by Douglas B. Staple

  I'm trying to understand limits to parallelization on a 48-core system (4xAMD Opteron 6348, 2.8 Ghz, 12 cores per CPU). I wrote this tiny OpenMP code to test the speedup in what I thought would be the best possible situation (the task is embarrassingly parallel): // Compile with: gcc scaling.c -std=c99 -fopenmp -O3 #include <stdio.h> #include <stdint.h> int main(){ const uint64_t umin=1; const uint64_t umax=10000000000LL; double sum=0.; #pragma omp parallel for reduction(+:sum) for(uint64_t u=umin; u<umax; u++) sum+=1./u/u; printf("%e\n", sum); } I was surprised to find that the scaling is highly nonlinear. It takes about 2.9s for the code to run with 48 threads, 3.1s with 36 threads, 3.7s with 24 threads, 4.9s with 12 threads, and 57s for the code to run with 1 thread. Unfortunately I have to say that there is one process running on the computer using 100% of one core, so that might be affecting it. It's not my process, so I can't end it to test the difference, but somehow I doubt that's making the difference between a 19~20x speedup and the ideal 48x speedup. To make sure it wasn't an OpenMP issue, I ran two copies of the program at the same time with 24 threads each (one with umin=1, umax=5000000000, and the other with umin=5000000000, umax=10000000000). In that case both copies of the program finish after 2.9s, so it's exactly the same as running 48 threads with a single instance of the program. What's preventing linear scaling with this simple program?

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• MySQL Locking Up

  - by Ian

  I've got a innodb table that gets a lot of reads and almost no writes (like, 1 write for every 400,000 reads approx). I'm running into a pretty big problem though when I do INSERT into the table. MySQL completely locks up. It uses 100% cpu, and every single other table (in other databases even) have their statuses set to "Locked" until the INSERT is done. This is a big problem because MySQL stays locked up for up to 4 minutes. I'm using version 5.1.47 (rpm from mysql.com). Any ideas?

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• Which memory related Tomcat JVM startup parameters are worth tuning?

  - by knorv

  I'm trying to understand the fine art of tuning Tomcat memory settings. In this quest I have the following three questions: Which memory related JVM startup parameters are worth setting when running Tomcat? Why? What are useful rule-of-thumbs when fine-tuning the memory settings for a Tomcat installation? How do you monitor the memory consumption of your live Tomcat installation?

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• What happens to a Redis data store if the data exceeds available ram?

  - by Chris Marisic

  What happens to a Redis data store if the data exceeds available ram?

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• PostgreSQL: Why does this simple query not use the index?

  - by David

  I have a table t with a column c, which is an int and has a btree index on it. Why does the following query not utilize this index? explain select c from t group by c; The result I get is: HashAggregate (cost=1005817.55..1005817.71 rows=16 width=4) -> Seq Scan on t (cost=0.00..946059.84 rows=23903084 width=4) My understanding of indexes is limited, but I thought such queries were the purpose of indexes.

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• receiving data from serialport stops when main form is minimized or moved

  - by Rahul

  Sir, I apologize if this is already covered somewhere. I did a search and find something which I have already implemented. I am developing an application which receives data from a device connected via serialport. I am using SerialPort datareceived event to capture data. I am to display data in text boxes of the main form. Data is received frequently. I used Timer to send command to the device, in response device send some data. Timer interval is 100 ms. In every 100 ms interval some command is sent and correspondingly data is received. I used Invoke function to update the GUI elements like TExtbox, labels etc. Everything is fine. All the elements are updating beautifully. But during receiving data if I make any change in main form like moving form, minimizing, maximizing, or clicking somewhere in the form, then data receiving stops. I couldnot find the reason why its happening ? I also changed the timer interval to 200,300,400,500 but same problem is there. Please tell me why its happening? And possible solution... Thanks In advance.... :)

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• Import 5 millions records to the rails application

  - by Bogdan Gusiev

  We need to import large amount of data(about 5 millions records) to the postgresql db under rails application. Data will be provided in xml format with images inside it encoded with Base64. Estimated size of the xml file is 40GB. What xml parser can handle such amount of data in ruby? Thanks.

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• Learn Fundamentals of Silverlight 4 Data Binding

  - by Eric J.

  I'm just starting to work with Silverlight (no WPF experience either) and am having a difficult time finding a source that provides a full explanation of Data Binding. There is absolutely no lack of tutorials (starting with the ones on Silverlight.net or Scott Gu's blogs), but everything I have found is "by example". Is there a resource that explains how data binding works in Silverlight, from a Fundamental/Conceptual perspective, and provides end-to-end coverage of data binding features? The desire for a more fundamental source of information is driven by a number of questions that came up this afternoon in reviewing tutorials and writing sample apps, such as: Why can't I bind the value of a slider like this?: Value="{Binding=Age, Mode=TwoWay}" where Age refers to an int property in the object data context I bind in code-behind (the Visual Studio error message is Expected '[]'. How do I use the DataContext property in VS 2010? What's a Path, Relative Source, Static Source, ...?

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• Why are compilers so stupid?

  - by martinus

  I always wonder why compilers can't figure out simple things that are obvious to the human eye. They do lots of simple optimizations, but never something even a little bit complex. For example, this code takes about 6 seconds on my computer to print the value zero (using java 1.6): int x = 0; for (int i = 0; i < 100 * 1000 * 1000 * 1000; ++i) { x += x + x + x + x + x; } System.out.println(x); It is totally obvious that x is never changed so no matter how often you add 0 to itself it stays zero. So the compiler could in theory replace this with System.out.println(0). Or even better, this takes 23 seconds: public int slow() { String s = "x"; for (int i = 0; i < 100000; ++i) { s += "x"; } return 10; } First the compiler could notice that I am actually creating a string s of 100000 "x" so it could automatically use s StringBuilder instead, or even better directly replace it with the resulting string as it is always the same. Second, It does not recognize that I do not actually use the string at all, so the whole loop could be discarded! Why, after so much manpower is going into fast compilers, are they still so relatively dumb? EDIT: Of course these are stupid examples that should never be used anywhere. But whenever I have to rewrite a beautiful and very readable code into something unreadable so that the compiler is happy and produces fast code, I wonder why compilers or some other automated tool can't do this work for me.

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• A solution for the slow diff in (Tortoise)SVN?

  - by Michal Czardybon

  I often do code review in the following way: Open the SVN log Select a revision Double click on a file... ...and wait See the changes Goto 2 or 3 or finish The 4th step is very annoying. Do you know a solution for this?

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• how to design this relation in a DB schema

  - by raticulin

  I have a table Car in my db, one of the columns is purchaseDate. I want to be able to tag every car with a number of Policies (limited to 10 policies). Each policy has a time to life (ttl, a duration of time, like '5 years', '10 months' etc), that is, for how long since the car's purchaseDate the policy can be applied. I need to perform the following actions: when inserting a Car, it will be set with a number of Policies (at least one is set) sometimes a Car will be updated to add/remove a Policy searches must be done taking into account date/policies, for example: 'select all cars that are not covered by any policy as of today' My current design is (pol0..pol9 are the policies): CREATE TABLE Car ( id int NOT NULL IDENTITY(1,1), purchaseDate datetime NOT NULL, //more stuff... pol0 smallint default NULL, pol1 smallint default NULL, pol2 smallint default NULL, pol3 smallint default NULL, pol4 smallint default NULL, pol5 smallint default NULL, pol6 smallint default NULL, pol7 smallint default NULL, pol8 smallint default NULL, pol9 smallint default NULL, PRIMARY KEY (id) ) CREATE TABLE Policy ( id smallint NOT NULL, name varchar(50) collate Latin1_General_BIN NOT NULL, ttl varchar(100) collate Latin1_General_BIN NOT NULL, PRIMARY KEY (id) ) The problem I am facing is that the sql to perform the query above is a nightmare to write. As I don't know in which column each policy can be, so I have to check all columns for every policy etc etc. So I am wondering wether it is worth changing this. My questions are: The smallint as Policy id was chosen instead of an 'int IDENTITY' in order to save some space as there are going to be millions of Car records. It just adds complexity when creating a Policy as we must handle the id etc. Was it worth doing this? I am thinking that maybe there is a much better design? Obviously we could move the policy/car relation to its own table CarPolicy, benefits would be: no limit on 10 policies per car adding/removing etc much easier when only the default policy is applied (when no others are applied one called Default policy is applied), we could signal that by not having any entry in CarPolicy, now this is just done inserting the Default policy id in one of the columns. The cons are that we would need to change the DB, ORM classes etc. What would you recommend? Maybe there is another smart way to implement this that we are not aware without using the CarPolicy table?

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• Mahout Recommendations on Binary data

  - by Pranay Kumar

  Hi, I'm a newbie to mahout.My aim is to produce recommendations on binary user purchased data.So i applied item-item similarity model in computing top N recommendations for movie lens data assuming 1-3 ratings as a 0 and 4-5 ratings as a 1.Then i tried evaluating my recommendations with the ratings in the test-data but hardly there have been two or three matches from my top 20 recommendations to the top rated items in test data and no match for most users. So are my recommendations totally bad by nature or do i need to go for a different measure for evaluating my recommendations ? Please help me ! Thanks in advance. Pranay, 2nd yr ,UG student.

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• jquery binding multiple events, and pass data

  - by mkoryak

  I know we can have this in 1.4: $("a").bind({ click : clickFn, mouseover: mouseFn }); and that is nice and i would like to use it, but it seems like there is no way to pass extra data to events bound this way, it needs to be done the 'old way': $("a").bind("click", {"some":"data"}, clickFn); Question: how can i pass the extra data to my event call backs and bind multiple events in a single bind at the same time?

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• Is it true "JavaScript files are not reliably cached by browsers, CSS files are"

  - by metal-gear-solid

  as mentioned on this site Note that while JavaScript files are not reliably cached by browsers, CSS files are. http://www.websiteoptimization.com/speed/tweak/http/

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• how to send data to server using python

  - by Apache

  hi experts, how data can be send to the server, for example i retrieve MAC address, so i want send to the server ( i.e 211.21.24.43:8080/data?mac=00-0C-F1-56-98-AD i found snippet from internet as below from urllib2 import Request, urlopen from binascii import b2a_base64 def b64open(url, postdata): req = Request(url, b2a_base64(postdata), headers={'Content-Transfer-Encoding': 'base64'}) return urlopen(req) conn = b64open("http://211.21.24.43:8080/data","mac=00-0C-F1-56-98-AD") but when run, File "send2.py", line 8 SyntaxError: Non-ASCII character '\xc3' in file send2.py on line 8, but no encoding declared; see http://www.python.org/peps/pep-0263.html for details can anyone help me how send data to the server thanks in advance

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• How do polymorphic inline caches work with mutable types?

  - by kingkilr

  A polymorphic inline cache works by caching the actual method by the type of the object, in order to avoid the expensive lookup procedures (usually a hashtable lookup). How does one handle the type comparison if the type objects are mutable (i.e. the method might be monkey patched into something different at run time). The one idea I've come up with would be a "class counter" that gets incremented each time a method is adjusted, however this seems like it would be exceptionally expensive in a heavily monkey patched environ since it would kill all the PICs for that class, even if the methods for them weren't altered. I'm sure there must be a good solution to this, as this issue is directly applicable to Javascript and AFAIK all 3 of the big JS VMs have PICs (wow acronym ahoy).

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• jQuery AJAX get request - cannot see returned data

  - by Wes

  I think I am missing something obvious here, but I can't figure it out. I expect the following HTML to alert a response from the server. But, the alert is empty. I can see in Wireshark that the expected response is coming back to me from the server. Why is it not populated in the data variable? <html> <head> <script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.4.2/jquery.min.js"></script> </head> <body> <script type="text/javascript"> $.get("http://www.geocommunicator.gov/TownshipGeocoder/TownshipGeocoder.asmx/GetTRS", {'Lat': 41, 'Lon': -93, 'Units': 'eDD', 'Datum': ''}, function(data) { alert('data:'+data); }); </script> </body> </html>

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• MSSQL Server high CPU and I/O activity database tuning

  - by zapping

  Our application tends to be running very slow recently. On debugging and tracing found out that the process is showing high cpu cycles and SQL Server shows high I/O activity. Can you please guide as to how it can be optimised? The application is now about an year old and the database file sizes are not very big or anything. The database is set to auto shrink. Its running on win2003, SQL Server 2005 and the application is a web application coded in c# i.e vs2005

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• How do I make this nested for loop, testing sums of cubes, more efficient?

  - by Brian J. Fink

  I'm trying to iterate through all the combinations of pairs of positive long integers in Java and testing the sum of their cubes to discover if it's a Fibonacci number. I'm currently doing this by using the value of the outer loop variable as the inner loop's upper limit, with the effect being that the outer loop runs a little slower each time. Initially it appeared to run very quickly--I was up to 10 digits within minutes. But now after 2 full days of continuous execution, I'm only somewhere in the middle range of 15 digits. At this rate it may end up taking a whole year just to finish running this program. The code for the program is below: import java.lang.*; import java.math.*; public class FindFib { public static void main(String args[]) { long uLimit=9223372036854775807L; //long maximum value BigDecimal PHI=new BigDecimal(1D+Math.sqrt(5D)/2D); //Golden Ratio for(long a=1;a<=uLimit;a++) //Outer Loop, 1 to maximum for(long b=1;b<=a;b++) //Inner Loop, 1 to current outer { //Cube the numbers and add BigDecimal c=BigDecimal.valueOf(a).pow(3).add(BigDecimal.valueOf(b).pow(3)); System.out.print(c+" "); //Output result //Upper and lower limits of interval for Mobius test: [c*PHI-1/c,c*PHI+1/c] BigDecimal d=c.multiply(PHI).subtract(BigDecimal.ONE.divide(c,BigDecimal.ROUND_HALF_UP)), e=c.multiply(PHI).add(BigDecimal.ONE.divide(c,BigDecimal.ROUND_HALF_UP)); //Mobius test: if integer in interval (floor values unequal) Fibonacci number! if (d.toBigInteger().compareTo(e.toBigInteger())!=0) System.out.println(); //Line feed else System.out.print("\r"); //Carriage return instead } //Display final message System.out.println("\rDone. "); } } Now the use of BigDecimal and BigInteger was delibrate; I need them to get the necessary precision. Is there anything other than my variable types that I could change to gain better efficiency?

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