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# Questions tagged [random]

This tag is for questions dealing with random numbers, pseudorandom numbers, and computer entropy.

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153 views

### Random Numbers and Collisions [closed]

I read a question about using a 32bit random number as a "unique" identifier. One of the answers asserted that a "rough guide" to estimating collision likelihood is that there's a ...
1 vote
1k views

### How to shuffle a large data set without touching every row?

Let’s say I have two larges arrays of users with equals number of rows and I want to match them randomly and one to one(one from the first array,one from the second), I will first need to shuffle one ...
790 views

### Can an 81 digit number generator lead to copyright infringement? [closed]

I'm looking to write a program that will generate valid sudoku puzzles. Essentially, a sudoku puzzle is just an 81 digit number. (The blanks are zeroes.) I would then like to use these puzzles in an ...
28k views

### Original source of `(seed * 9301 + 49297) % 233280` random algorithm?

If you search for examples of creating a seeded (pseudo)Random number generator, you will run into stuff like this (specific example http://indiegamr.com/generate-repeatable-random-numbers-in-js/): //...
459 views

### random.choice in other languages

Python has a nice function in the standard library random.choice which returns a random element from a sequence. But none of the other languages I've developed in have thought to include such a ...
5k views

### Generate unique integer from two integers with algorithm

I am currently trying to come up with an algoritm which would take at least two numbers (say user IDs) and then come up with an unique number which is generated based on these two numbers. Each ...
15k views

### How to generate "language-safe" UUIDs?

I always wanted to use randomly generated strings for my resources' IDs, so I could have shorter URLs like this: /user/4jz0k1 But I never did, because I was worried about the random string generation ...
1k views

### What are best practices for testing programs with stochastic behavior?

Doing R&D work, I often find myself writing programs that have some large degree of randomness in their behavior. For example, when I work in Genetic Programming, I often write programs that ...
1k views

### Is checking if a new GUID exists before insert a code smell?

Say I use GUIDs as keys. Considering the chance of a duplicate GUID being generated being what they are, is code like this considered a code smell? Guid newID = GenerateGuid(); while (dictionary....
767 views

### What are the reasons not to use random values in unittests? [duplicate]

I've read the questions regarding the use of random values in unit-tests and, well, I still don't quite understand what the argument against random values is. I'm trying to understand because I've had ...
284 views

### Improving performance of 'Weighted/prioritized left shuffle algorithm'

I wrote a prioritized/weighted left shuffle algorithm (the code is copied from my open source C# project Fluent Random Picker). What does that mean? You've got some values and each of them has a ...
1 vote
220 views

### Randomly sorting a list where some states are illegal?

I want to make a randomizer for the items in the game La-Mulana. However, some arrangements of items would mean that the game cannot be completed. Sometimes there's only one group of items required to ...
55k views

### get weighted random item

I have, for example, this table +-----------------+ | fruit | weight | +-----------------+ | apple | 4 | | orange | 2 | | lemon | 1 | +-----------------+ I need to return a random ...
779 views

### How does cuRAND use a GPU to accelerate random number generation? Don't those require a state?

My understanding is that every PRNG or QRNG requires a state to prevent the next item in its sequence from being too predictable; which is sensible, as they're all running on deterministic hardware. ...
227 views

### How random is enough to be random? [closed]

I download the atmospheric noise data from random.org in form: 10111011 01101111 01100001 00001001 00100110 10111011 01110110 11010110 00000111 01111110 10001110 01101010 11100000 11110111 10101011 ...
79 views

### How to write a sporadic metronome?

I already asked this question on stackoverflow -- I am posting it here as well, because I think many of you will have encountered an analogous problem. I would appreciate even a link as a reference, ...
1 vote
1k views

### Is using multiple UUIDs decrease chance of collisions exponentially?

For example if you have a single UUID with a collision probability of x, if you concatenate 2 UUIDs, does the collision probability become x^2? val0 = generate_uuid() val1 = generate_uuid() final_val ...
883 views

### How to guarantee an ID is unique in a non-UUID set of values?

I would like to have IDs of different sizes from the alphabet 0-9. So I have 5-length IDs as in 10000 or 13531, etc.. I have 10, 15, 20, up to 39 digit strings (the size of a UUID). I would like to ...
99k views

### How should I test randomness?

Consider a method to randomly shuffle elements in an array. How would you write a simple yet robust unit test to make sure that this is working? I've come up with two ideas, both of which have ...
809 views

### Algorithm for random weighted boolean shuffles?

I don't exactly know how to phrase the thing I'm searching for in a succinct way, which also made it hard to research. In my application I need a random list of booleans, say of length five. The ...
2k views

### Random Cache Expiry

I've been experimenting with random cache expiry times to avoid situations where an individual request forces multiple things to update at once. For example, a web page might include five different ...
548 views

### Is it really more difficult to debug randomized algorithms?

I am a theoretical computer scientist. I have heard the following: Practitioners do not like randomized algorithms because they are notoriously difficult to debug. So deterministic algorithms are ...
3k views

### Shuffle in music players

I always hear how it is hard to implement shuffle algorithms for music players, but never really the explanation for it. What makes it hard? Take for example how I would implement one: First the ...
116 views

### Is it possible to transfer data with a really unique seed of a psudo random number generator

I have thinking about this idea for over 5 years and i don't have the complete technical knowledge to fully grasp the idea I'm having. The premise of the idea is to have an extremely high base number ...
10k views

### Unit-testing of inherently random/non-deterministic algorithms

My current project, succinctly, involves the creation of "constrainably-random events". I'm basically generating a schedule of inspections. Some of them are based on strict schedule constraints; you ...
349 views

### Getting random yet consistent data for testing

I have a big codebase yet to be covered with tests and rather limited access to the real data. The code that needs to be covered is very data dependent. And the data is anything but shallow and ...
328 views

### Choosing random cards from a deck?

Is there a difference between the 2 below methods for choosing a random card from a deck of cards? Is one approach more accepted than the other? Method 1: Generate a random number from 1-52 for the ...
586 views

### Unit testing Markov chain code

What are the best ways to unit test code that outputs random sequences satisfying specific conditions, such as Markov chains? Let's be specific. There are two natural things to test: That the ...
2k views

### Generating billions of Unique random number [closed]

I recently attended an interview. In that I had to solve the issue for generating an billions of random unique number. For example method signature is as below : public Iterator<Long> ...
313 views

### Are all pseudo randomly generated numbers within a given period unique?

This will of course depend on the algorithm generating the pseudo random numbers, but what I'm wondering is whether practical, usable pseudo-random number generating algorithms exist that never repeat ...
885 views

### Can functional programming used for solving problems which require randomness?

This older question tells us that in functional programming "true" randomness cannot be achieved since in FP functions are pure/idempotent and return the same value irrespective of number of ...
12k views

### I need a true random number generator web service [closed]

Random.org provides 200k free random bits (only 6250 32-bit integers!) from the analog world (cf.) per IP per day. Does anyone know of an alternative web service that provides more on-demand random ...
10k views

### random generator not good enough?

During an interview I was asked to implement a random generator in java without using any existing random number libraries that takes as an argument int n, and returns a random number between 0 and n. ...
223 views

### How to test this getRandom() method? [duplicate]

There are strings and each string has a weight in a data structure. The getRandom() method should return a string randomly with its weight/total weight probability. There is already a question on how ...
35k views

### Testing a function that uses random number generator

I have a method which is a part of the interface I am implementing. This method calls another private method which uses a random number generator to produce output and returns it to the calling method....
351 views

### Find Randomized Sequence Seed To Compress files statistically

I was wondering if what I have in mind already exists in any known compression programs/algorithms or not. We know that Seed gives us constant sequence of random numbers. so if we be able to find seed ...
2k views

### Is generating a large random number more unique than generating each digit in that number?

I'm using a PRNG (PHP's default rand() implementation) to generate unique 16 digit numbers. Does it make sense to generate digits one by one, or the number at once? I'm using PHP.
170 views

### Restricted randomization of a binary vector

Suppose I have a binary vector of sample size N with each of the two possible values (e.g., 0 and 1 occurring equally often). For example, if N=10, the binary vector is: 0 0 0 0 0 1 1 1 1 1 Suppose ...
782 views

### Test Driven Development for Stochastic algorithms?

this is similar, but no the same as this post, which was the closest question I could find on this. I don't even see that answer as satisfactory for the question asked in that thread let alone TDD. ...
1 vote
102 views

### Disk file structure for large string list with fast reads by index

I have large list of strings. Each string is of different length, just like sentence in text. Average length is below 255 chars. Please, propose file structure on disk to enable fast picking of random ...
117k views

### How do random number generators work?

I was just pondering about php rand() function, and thinking about how I could remake it, and I came up completely stupified. How do random number generators work?
828 views

### How to generate a random bag of positive integers that sum up to an input number?

A number N and a range a to b will be input by the user, with a < b < N. The program purpose is to generate random sets of positive integers that sum up to N, with each positive integers within ...
293 views

### Is a random sample from a range of uniformly distributed values still uniformly distributed?

Let's say I have a random number generator from which I am requesting values for event A and event B. Both events occur at random intervals but event A happens much more often than event B and I would ...
4k views

### Since Garbage Collection is non-deterministic, why isn't it used for secure random number generation?

I get that /dev/random is a good source of entropy, and is what is usually used-- It's just as I'm reading up on GC, at least in Java, it seems accepted that the garbage collection daemon executes non-...
827 views

### Flowchart: get values from functions. Rectangle or Paralellogram

I need to create a flowchart for one of my algorithms and one step is calling a function (that I don't wish to explain in the flowchart) and assigning the returned value to a variable. float x = ...
1k views

### Programming a Truly "Fair" Weighted Random Dice Roll

I'm trying to devise a way to create a 'loot table' for an RPG, mostly to see if it can be done. I'm partly inspired by old D&D style tables, which would list a range of values for each item on ...
130 views

### Return random item by its weight, advanced level

There are many typical questions like Return random `list` item by its `weight` Imagine more advanced problem. You have N sources of pair (item_id, weight) information. Let's call them Shards. ...
11k views

### How to generate random numbers without making new Random objects?

I'm using this as part of a game, but it's not really a game development question, so I'm putting it on this more general Stack Exchange. The goal is to generate "random" outputs for a fixed integer ...