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• only return random number when it is unique

  - by phil

  My brain is melting today and i cannot think how to do this simple bit of code. numberList is a string of numbers seperated by commas like '2, 34, 10' etc.. when i request a random number i need to check if the string has the number, if it does i want to keep requesting a random number until the random number is definitely not in the string. i cant think what kind of loop i would do to get this to work: Random r = new Random(); public int RandomPos(int max) { int i; do { i = r.Next(max) + 1; } while (!numberList.Contains(i.ToString())); return i; }

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• Could random.randint(1,10) ever return 11?

  - by Tim Pietzcker

  When researching for this question and reading the sourcecode in random.py, I started wondering whether randrange and randint really behave as "advertised". I am very much inclined to believe so, but the way I read it, randrange is essentially implemented as start + int(random.random()*(stop-start)) (assuming integer values for start and stop), so randrange(1, 10) should return a random number between 1 and 9. randint(start, stop) is calling randrange(start, stop+1), thereby returning a number between 1 and 10. My question is now: If random() were ever to return 1.0, then randint(1,10) would return 11, wouldn't it?

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• Choosing random numbers efficiently

  - by Frederik Wordenskjold

  I have a method, which uses random samples to approximate a calculation. This method is called millions of times, so its very important that the process of choosing the random numbers is efficient. I'm not sure how fast javas Random().nextInt really are, but my program does not seem to benefit as much as I would like it too. When choosing the random numbers, I do the following (in semi pseudo-code): // Repeat this 300000 times Set set = new Set(); while(set.length != 5) set.add(randomNumber(MIN,MAX)); Now, this obviously has a bad worst-case running time, as the random-function in theory can add duplicated numbers for an eternity, thus staying in the while-loop forever. However, the numbers are chosen from {0..45}, so a duplicated value is for the most part unlikely. When I use the above method, its only 40% faster than my other method, which does not approximate, but yields the correct result. This is ran ~ 1 million times, so I was expecting this new method to be at least 50% faster. Do you have any suggestions for a faster method? Or maybe you know of a more efficient way of generation a set of random numbers.

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• Two different seeds producing the same "random" sequence

  - by Ruud Lenders

  Maybe there is a very logic explanation for this, but I just can't seem to understand why the seeds 0 and 2,147,483,647 produce the same "random" sequence, using .NET's Random Class (System). Quick code example: ushort len = 8; Random r0 = new Random(0), r1 = new Random(1), r2 = new Random(int.MaxValue); //2,147,483,647 byte[] b0 = new byte[len], b1 = new byte[len], b2 = new byte[len]; r0.NextBytes(b0); r1.NextBytes(b1); r2.NextBytes(b2); for (int i = 0; i < len; i++) { System.Diagnostics.Debug.WriteLine("{0}\t\t{1}\t\t{2}", b0[i], b1[i], b2[i]); } Console.ReadLine(); Output: 26 70 26 12 208 12 70 134 76 111 130 111 93 64 93 117 151 115 228 228 228 216 163 216 As you can see, the first and the third sequence are the same. Can someone please explain this to me?

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• Same random numbers from instantiated class

  - by user1797202

  I'm learning C# and created a class within my program that holds a random number generator: class RandomNumberGenerator { Random RNG = new Random(); // A bunch of methods that use random numbers are in here } Inside this class are a few methods that use the RNG. Data gets sent here from other parts of the program, gets processed, then gets returned. One of the methods does the following: // Method works something like this int Value1 = RNG.Next(x, y); int Value2 = RNG.Next(x, y); int Value3 = RNG.Next(x, y); The x, y values are to be sent here from another class. So, I have to create an instance of the RandomNumberGenerator within that class so I can call its methods and pass the x and y values to it. class DoStuff { RandomNumberGenerator Randomizer = new RandomNumberGenerator // Here I call a bunch of Randomizer methods that give me values I need } The problem in the above method is that I get the same numbers every time for all three values. I'm not sure if it's because they're so close together and Randomizer's seed value hasn't had time to change or if I'm doing something wrong when I create a new instance of the RandomNumberGenerator class. I've gone through a bunch of answers on here already and typically problems like this are due to people creating many new Random objects when they run methods (thus setting the seed for all of them to the same value), but the only new Random object I create is within the RandomNumberGenerator class. I then instantiate that once within the other class so I can pass it data and use its methods. Why is this happening and how would I fix this?

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• iDVD Random Transitions

  - by mracoker

  I am creating a dvd slide show using iDVD and I see how to add transtions manually but what I would like to do is have iDVD insert random transitions for me. Is this possible?

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• What's a good algorithm for a random, uneven distribution of a fixed amount of a resource?

  - by NickC

  Problem I have X, a positive integer, of some resource, R. There are N potential targets. I want to distribute all of R to the N targets in some "interesting" way. "Interesting" means: Some targets may not get any R. It should rarely be near even (with a majority of target getting near X/N of the resource). There should be at least a small chance of one target getting all of R. Bad solutions The naive approach would be to pick a random target and give one R to it and repeat X times. This would result in too even of an approach. The next idea is to pick a random number between 1 and X and give it to a random target. This results in too large of a number (at least X/2 on average) being given to one target. Question This algorithm will be used frequently and I want the distribution to be interesting and uneven so that the surprise doesn't wear off for users. Is there a good algorithm for something in between these two approaches, that fits the definition of interesting above?

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• How Random is System.Guid.NewGuid()? (Take two)

  - by Vilx-

  Before you start marking this as a duplicate, read me out. The other question has a (most likely) incorrect accepted answer. I do not know how .NET generates its GUIDs, probably only Microsoft does, but there's a high chance it simply calls CoCreateGuid(). That function however is documented to be calling UuidCreate(). And the algorithms for creating an UUID are pretty well documented. Long story short, be as it may, it seems that System.Guid.NewGuid() indeed uses version 4 UUID generation algorithm, because all the GUIDs it generates matches the criteria (see for yourself, I tried a couple million GUIDs, they all matched). In other words, these GUIDs are almost random, except for a few known bits. This then again raises the question - how random IS this random? As every good little programmer knows, a pseudo-random number algorithm is only as random as its seed (aka entropy). So what is the seed for UuidCreate()? How ofter is the PRNG re-seeded? Is it cryptographically strong, or can I expect the same GUIDs to start pouring out if two computers accidentally call System.Guid.NewGuid() at the same time? And can the state of the PRNG be guessed if sufficiently many sequentially generated GUIDs are gathered?

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• Apache2 random 403 error & info server busy logs on Ubuntu

  - by risyasin

  Hello, I have a strange situation with apache2. Meanless, random 403 errors. Any page (html, php etc.) normally working. but if i request repeatedly by pressing refresh button of browser. it interrupts & sends a 403 randomly. after a few seconds it works again. in the error log, i see client denied by server configuration. main error log of apache says [info] server seems busy, (you may need to increase StartServers, or Min/MaxSpareServers), spawning 8 children, there are 99 idle, and 137 total children my current values IfModule mpm_prefork_module StartServers 120 MinSpareServers 100 MaxSpareServers 200 MaxClients 256 MaxRequestsPerChild 500 /IfModule i've increased 10 by 10. from 20. but nothing solved. i've disabled KeepAlive. What may cause this problem ? thank you in advance. a fresh install Ubuntu server x86 8.04.4 Virtualmin from it's website (not from debian repositories). Linux 2.6.24-27-server #1 SMP i686 - Apache 2.2.8 Mpm prefork Virtualmin version 3.78.gpl GPL PHP Version 5.2.4-2ubuntu5.10 Loaded modules: core_module (static) log_config_module (static) logio_module (static) mpm_prefork_module (static) http_module (static) so_module (static) actions_module shared) alias_module (shared) auth_basic_module (shared) auth_digest_module (shared) uthn_file_module (shared) authz_default_module (shared) authz_groupfile_module (shared) uthz_host_module (shared) authz_user_module (shared) autoindex_module (shared) ache_module shared) cgi_module (shared) deflate_module (shared) dir_module (shared) env_module (shared) expires_module (shared) fcgid_module (shared) file_cache_module (shared) eaders_module (shared) mime_module (shared) mime_magic_module (shared) evasive20_module shared) negotiation_module (shared) php5_module (shared) rewrite_module (shared) etenvif_module (shared) ssl_module (shared) status_module (shared) Syntax OK

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• How to generate random number with the specific length in python

  - by Arty

  Let say I need a 3 digit number, so it would be something like: >>> random(3) 563 or >>> random(5) 26748 >> random(2) 56

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• module "random" not found when building .exe from IronPython 2.6 script

  - by Graham

  I am using SharpDevelop to build an executable from my IronPython script. The only hitch is that my script has the line import random which works fine when I run the script through ipy.exe, but when I attempt to build and run an exe from the script in SharpDevelop, I always get the message: IronPython.Runtime.Exceptions.ImportException: No module named random Why isn't SharpDevelop 'seeing' random? How can I make it see it?

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• Reversible pseudo-random sequence generator

  - by user350651

  I would like some sort of method to create a fairly long sequence of random numbers that I can flip through backwards and forwards. Like a machine with "next" and "previous" buttons, that will give you random numbers. Something like 10-bit resolution (i.e. positive integers in a range from 0 to 1023) is enough, and a sequence of 100k numbers. It's for a simple game-type app, I don't need encryption-strength randomness or anything, but I want it to feel fairly random. I have a limited amount of memory available though, so I can't just generate a chunk of random data and go through it. I need to get the numbers in "interactive time" - I can easily spend a few ms thinking about the next number, but not comfortably much more than that. Eventually it will run on some sort of microcontroller, probably just an Arduino. I could do it with a simple linear congruential generator (LCG). Going forwards is simple, to go backwards I'd have to cache the most recent numbers and store some points at intervals so I can recreate the sequence from there. But maybe there IS some pseudo-random generator that allows you to go both forwards and forwards? It should be possible to hook up two linear feedback shift registers (LFSRs) to roll in different directions, no? Or maybe I can just get by with garbling the index number using a hash function of some sort? I'm going to try that first. Any other ideas?

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• Best way to choose a random file from a directory in a shell script

  - by jhs

  What is the best way to choose a random file from a directory in a shell script? Here is my solution in Bash but I would be very interested for a more portable (non-GNU) version for use on Unix proper. dir='some/directory' file=`/bin/ls -1 "$dir" | sort --random-sort | head -1` path=`readlink --canonicalize "$dir/$file"` # Converts to full path echo "The randomly-selected file is: $path" Anybody have any other ideas? Edit: lhunath makes a good point about parsing ls. I guess it comes down to whether you want to be portable or not. If you have the GNU findutils and coreutils then you can do: find "$dir" -maxdepth 1 -mindepth 1 -type f -print0 \ | sort --zero-terminated --random-sort \ | sed 's/\d000.*//g/' Whew, that was fun! Also it matches my question better since I said "random file". Honsetly though, these days it's hard to imagine a Unix system deployed out there having GNU installed but not Perl 5.

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• Join a single row in one table to n random rows in another

  - by Einar Egilsson

  Is it possible to make a join in SQL server that joins each row from table A to n random rows in another? For example, say I have a Customer table, a Product table and an Order table. I want to join each customer to 5 random products and insert these rows into the order table. (And each customer should be joined to 5 random rows of his own, I don't want all customers joining to the same 5 rows). Is this possible? I'm using SQL Server 2005 and it's fine if the solution is specific to that. This is a weird requirement but I'm basically making a small data generator to generate some random data.

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• Getting random record from database with group by

  - by Saif Bechan

  Hello i have a question on picking random entries from a database. I have 4 tables, products, bids and autobids, and users. Products ------- id 20,21,22,23,24(prime_key) price........... etc........... users ------- id(prim_key) name user1,user2,user3 etc bids ------- product_id user_id created autobids -------- user_id product_id Now a multiple users can have an autobid on an product. So for the next bidder I want to select a random user from the autobid table example of the query in language: for each product in the autobid table I want a random user, which is not the last bidder. On product 20 has user1,user2,user3 an autobidding. On product 21 has user1,user2,user3 an autobidding Then I want a resultset that looks for example like this 20 – user2 21 – user3 Just a random user. I tried miximg the GOUP BY (product_id) and making it RAND(), but I just can't get the right values from it. Now I am getting a random user, but all the values that go with it don't match. Can someone please help me construct this query, I am using php and mysql

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• Random forests for short texts

  - by Jasie

  Hi all, I've been reading about Random Forests (1,2) because I think it'd be really cool to be able to classify a set of 1,000 sentences into pre-defined categories. I'm wondering if someone can explain to me the algorithm better, I think the papers are a bit dense. Here's the gist from 1: Overview We assume that the user knows about the construction of single classification trees. Random Forests grows many classification trees. To classify a new object from an input vector, put the input vector down each of the trees in the forest. Each tree gives a classification, and we say the tree "votes" for that class. The forest chooses the classification having the most votes (over all the trees in the forest). Each tree is grown as follows: If the number of cases in the training set is N, sample N cases at random - but with replacement, from the original data. This sample will be the training set for growing the tree. If there are M input variables, a number m « M is specified such that at each node, m variables are selected at random out of the M and the best split on these m is used to split the node. The value of m is held constant during the forest growing. Each tree is grown to the largest extent possible. There is no pruning. So, does this look right? I'd have N = 1,000 training cases (sentences), M = 100 variables (let's say, there are only 100 unique words across all sentences), so the input vector is a bit vector of length 100 corresponding to each word. I randomly sample N = 1000 cases at random (with replacement) to build trees from. I pick some small number of input variables m « M, let's say 10, to build a tree off of. Do I build tree nodes randomly, using all m input variables? How many classification trees do I build? Thanks for the help!

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• Set seed on Math.random()

  - by Kevin

  Hi - I need to write some junit tests on java code that calls Math.random(). I know that I can set the seed if I was instantiating my own Random object to produce repeatable results. Is there a way to do this also for Math.random() ?

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• Random number in a loop

  - by Sam

  Hi all, having an issue generating random numbers in a loop. Can get around it by using Thread.Sleep but after a more elegant solution. for ... Random r = new Random(); string += r.Next(4); Will end up with 11111... 222... etc. Suggestions?

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• SQL SERVER – Retrieving Random Rows from Table Using NEWID()

  - by pinaldave

  I have previously written about how to get random rows from SQL Server. SQL SERVER – Generate A Single Random Number for Range of Rows of Any Table – Very interesting Question from Reader SQL SERVER – Random Number Generator Script – SQL Query However, I have not blogged about following trick before. Let me share the trick here as well. You can generate random scripts using following methods as well. USE AdventureWorks2012 GO -- Method 1 SELECT TOP 100 * FROM Sales.SalesOrderDetail ORDER BY NEWID() GO -- Method 2 SELECT TOP 100 * FROM Sales.SalesOrderDetail ORDER BY CHECKSUM(NEWID()) GO You will notice that using NEWID() in the ORDER BY will return random rows in the result set. How many of you knew this trick? You can run above script multiple times and it will give random rows every single time. Reference: Pinal Dave (http://blog.sqlauthority.com)   Filed under: PostADay, SQL, SQL Authority, SQL Function, SQL Query, SQL Server, SQL Tips and Tricks, T SQL, Technology

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• Java random values and duplicates

  - by f-Prime

  I have an array (cards) of 52 cards (13x4), and another array (cardsOut) of 25 cards (5x5). I want to copy elements from the 52 cards into the 25 card array by random. Also, I dont want any duplicates in the 5x5 array. So here's what I have: double row=Math.random() *13; double column=Math.random() *4; boolean[][] duplicates=new boolean[13][4]; pokerGame[][] cardsOut = new pokerGame[5][5]; for (int i=0;i<5;i++) for (int j=0;j<5;j++){ if(duplicates[(int)row][(int)column]==false){ cardsOut[i][j]=cards[(int)row][(int)column]; duplicates[(int)row][(int)column]=true; } } 2 problems in this code. First, the random values for row and column are only generated once, so the same value is copied into the 5x5 array every time. Since the same values are being copied every time, I'm not sure if my duplicate checker is very effective, or if it works at all. How do I fix this?

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• random image and its url

  - by venom

  i want to create a random image and its url, i mean not the link of the image, but in addition to image's link, i want the specified URL, so that random image was displayed and when u click on it, u go to the specified URL here is my javascript: function random_imglink(){ var myimages=new Array() //specify random images below. You can have as many as you wish myimages[1]="/documents/templates/projedepo/banner/canon.jpg" myimages[2]="/documents/templates/projedepo/banner/indigovision.jpg" var ry=Math.floor(Math.random()*myimages.length) if (ry==0) ry=1 var randomImage = '<img src="'+myimages[ry]+'" height="420" width="964" />'; document.getElementById("image2").innerHTML = randomImage; } random_imglink() Here is my HTML: <div id="slider_container"> <div id="image2"> </div> <div id="thumb2"> <a href="#" rel="/documents/templates/projedepo/banner/canon.jpg" class="image2" ><img title="Canon" class="slider_thumb" src="/documents/templates/bilgiteknolojileri/images/t_flash/t1.png" border="0"/></a> <a href="#" rel="/documents/templates/projedepo/banner/indigovision.jpg" class="image2"><img title="IndogoVision" class="slider_thumb" src="/documents/templates/bilgiteknolojileri/images/t_flash/t2.png" border="0"/></a> </div></div>

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• Random Computer Crashes

  - by Josh W.

  Ok, here's a wierd one for you all. Occasionally my PC here at work will crash in a very peculiar way. My dual monitors will suddenly go blank as if there is no longer a video signal, the USB mouse light will go dark and mouse stays unresponsive, the keyboard lights will not change status when the appropriate keys are pressed (Num/Caps/Scoll Lock). The CD Tray WILL open and close. But the computer will not respond to a ping request. For all intents & purposes it's as if the computer is off, except it wasn't intentional by me. The power light and internal fans are still on and I've now lost any unsaved work. Now here's where it gets wierd. This PC is part of a batch of PC's we got from a local vendor who does our initial system builds. Mine, and 6 other co-workers PCs all have the same issue. Originally we thought it was a bad combination of hardware, but through trial and error the only thing we haven't eliminated are the OS, Mobo & CPU. The problem was so bad for some of them that they ended up going back to their 5 year old dinosaurs in order to get some work done, for me the problem isn't as bad, maybe once every other day or so, but still enough to bite me in the ass if I've forgotten my ritualistic pressing of CTRL-S every 1-5 minutes. In this case we've tried two different video cards, two different power supplies, two different memory configurations, running on a UPS/not on UPS, updating/rolling back video drivers, three different bios revisions. The only things we haven't swapped are the mobo & cpu, mainly because a new mobo means a new Hardware Abstraction Layer, ie re-install of windows and there's alot of other software on this PC that takes forever to reload by hand. There was a base image that our systems team created with all the drivers installed and the basic setup of software our company uses, but they then must customize the setup for us programmers so it takes a while to get a new configuration up and going. I'm a programmer by day and am usually pretty good at diagnosing computer problems whether through trial and error or not. We've pretty much exhausted all the ideas we can think of here, short of a new mobo/cpu. Was hoping someone out there might have anything else we can try.. Relevant Parts: OS: XP Pro 32-bit Motherboard: Intel DG41RQ CPU: Intel Core-2 Quad Q9400 @ 2.66GHz Current BIOS Version/Date Intel Corp. RQG4110H.86A.0014.2010.0306.1151, 3/6/2010 Dual LCD's, Viewsonic VG930m & Samsung SyncMaster 910v (other people have different models, but listed in case there's some very wierd problem with the signals being sent/received) PS/2 Keyboard USB Microsoft Intellimouse BIOS Versions Tried: R 0013 12/23/2009 R 0014 3/6/2010 Video cards Tried GeForce 8400 GS Radeon HD 4350 - ASUS EAH4350 Two Different Power Supplies a 380W & 550W Ram Configurations 2GB - 1 x 2GB 4GB - 2 x 2GB

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• Random Number on SQL without using NewID()

  - by Angel Escobedo

  Hello I want to generate a Unique Random number with out using the follow statement : Convert(int, (CHECKSUM(NEWID()))*100000) AS [ITEM] Cause when I use joins clauses on "from" it generates double registers by using NEWID() Im using SQL Server 2000 *PD : When I use Rand() it probably repeat on probability 1 of 100000000 but this is so criticall so it have to be 0% of probability to repeat a random value generated My Query with NewID() and result on SELECT statement is duplicated (x2) My QUery without NewID() and using Rand() on SELECT statement is single (x1) but the probability of repeat the random value generated is uncertainly but exists! Thanks!

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• Generating random numbers in C

  - by moonstruckhorrors

  While searching for Tutorials on generating random numbers in C I found This Topic When I try to use the rand() function with parameters, I always get the random number generated 0. When I try to use the rand() function with parameters, I always get the value 41. And whenever I try to use arc4random() and random() functions, I get a LNK2019 error. Here's what I'm doing: #include <stdlib.h> int main() { int x; x = rand(6); printf("%d", x); } This code always generate 41. Where am I going wrong?? P.S. : I'm running Windows XP SP3 and using VS2010 Command Prompt as compiler. P.P.S. : Took me 15 minutes to learn how to format properly.

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• Read random lines from huge CSV file in Python

  - by jbssm

  I have this quite big CSV file (15 Gb) and I need to read about 1 million random lines from it. As far as I can see - and implement - the CSV utility in Python only allows to iterate sequentially in the file. It's very memory consuming to read the all file into memory to use some random choosing and it's very time consuming to go trough all the file and discard some values and choose others, so, is there anyway to choose some random line from the CSV file and read only that line? I tried without success: import csv with open('linear_e_LAN2A_F_0_435keV.csv') as file: reader = csv.reader(file) print reader[someRandomInteger] A sample of the CSV file: 331.093,329.735 251.188,249.994 374.468,373.782 295.643,295.159 83.9058,0 380.709,116.221 352.238,351.891 183.809,182.615 257.277,201.302 61.4598,40.7106

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