All Questions
Tagged with probability random
574
questions
308
votes
23
answers
251k
views
Generate a random point within a circle (uniformly)
I need to generate a uniformly random point within a circle of radius R.
I realize that by just picking a uniformly random angle in the interval [0 ... 2π), and uniformly random radius in the ...
- 417k
148
votes
4
answers
15k
views
Data structures for loaded dice?
Suppose that I have an n-sided loaded die, where each side k has some probability pk of coming up when I roll it. I’m curious if there is a good data structure for storing this information statically (...
- 367k
140
votes
3
answers
10k
views
Why does this random value have a 25/75 distribution instead of 50/50?
Edit: So basically what I'm trying to write is a 1 bit hash for double.
I want to map a double to true or false with a 50/50 chance. For that I wrote code that picks some random numbers (just as an ...
- 19.3k
79
votes
14
answers
41k
views
Select k random elements from a list whose elements have weights
Selecting without any weights (equal probabilities) is beautifully described here.
I was wondering if there is a way to convert this approach to a weighted one.
I am also interested in other ...
- 10.2k
76
votes
13
answers
72k
views
How to pick an item by its probability?
I have a list of items. Each of these items has its own probability.
Can anyone suggest an algorithm to pick an item based on its probability?
- 9,816
68
votes
11
answers
86k
views
Random number with Probabilities
I am wondering what would be the best way (e.g. in Java) to generate random numbers within a particular range where each number has a certain probability to occur or not?
e.g.
Generate random ...
- 5,846
45
votes
7
answers
74k
views
Generate Random Boolean Probability
I only know how I can generate a random boolean value (true/false).
The default probability is 50:50
But how can I generate a true false value with my own probability?
Let's say it returns true with ...
- 705
38
votes
6
answers
50k
views
How can I make a random choice according to probabilities stored in a list (weighted random distribution)?
Given a list of probabilities like:
P = [0.10, 0.25, 0.60, 0.05]
(I can ensure that the sum of all the variables in P is always 1)
How can I write a function that randomly returns a valid index, ...
- 305
38
votes
10
answers
5k
views
An interview question: About Probability
An interview question:
Given a function f(x) that 1/4 times returns 0, 3/4 times returns 1.
Write a function g(x) using f(x) that 1/2 times returns 0, 1/2 times returns 1.
My implementation is:
...
- 15.7k
36
votes
7
answers
53k
views
How do I simulate flip of biased coin?
In unbiased coin flip H or T occurs 50% of times.
But I want to simulate coin which gives H with probability 'p' and T with probability '(1-p)'.
something like this:
def flip(p):
'''this ...
- 36.3k
30
votes
7
answers
35k
views
Generate random integers with probabilities
I'm a bit confused about how to generate integer values with probabilities.
As an example, I have four integers with their probability values: 1|0.4, 2|0.3, 3|0.2, 4|0.1
How can I generate these ...
- 21.3k
30
votes
8
answers
26k
views
Distributed probability random number generator
I want to generate a number based on a distributed probability. For example, just say there are the following occurrences of each numbers:
Number| Count
1 | 150
2 | ...
- 493
30
votes
9
answers
13k
views
How to do weighted random sample of categories in python
Given a list of tuples where each tuple consists of a probability and an item I'd like to sample an item according to its probability. For example, give the list [ (.3, 'a'), (.4, 'b'), (.3, 'c')] I'd ...
- 303
30
votes
8
answers
14k
views
Random boolean with weight or bias
I need to generate some random booleans. However I need to be able to specify the probability of returning true. As a results doing:
private Random random = new Random();
random.nextBoolean();
will ...
- 2,040
25
votes
7
answers
39k
views
Generate random number with given probability matlab
I want to generate a random number with a given probability but I'm not sure how to:
I need a number between 1 and 3
num = ceil(rand*3);
but I need different values to have different probabilities ...
- 8,936
23
votes
5
answers
47k
views
Algorithm to generate Poisson and binomial random numbers?
i've been looking around, but i'm not sure how to do it.
i've found this page which, in the last paragraph, says:
A simple generator for random numbers taken from a Poisson distribution is obtained ...
snap
23
votes
4
answers
24k
views
Probability Random Number Generator
Let's say I'm writing a simple luck game - each player presses Enter and the game assigns him a random number between 1-6. Just like a cube. At the end of the game, the player with the highest number ...
- 56.9k
21
votes
12
answers
21k
views
Probability distribution in Python
I have a bunch of keys that each have an unlikeliness variable. I want to randomly choose one of these keys, yet I want it to be more unlikely for unlikely (key, values) to be chosen than a less ...
20
votes
7
answers
12k
views
Unbiased random number generator using a biased one
You have a biased random number generator that produces a 1 with a probability p and 0 with a probability (1-p). You do not know the value of p. Using this make an unbiased random number generator ...
- 18.6k
19
votes
6
answers
12k
views
Generating N numbers that sum to 1
Given an array of size n I want to generate random probabilities for each index such that Sigma(a[0]..a[n-1])=1
One possible result might be:
0 1 2 3 4
0.15 0.2 0.18 0.22 0.25
...
- 163k
18
votes
2
answers
2k
views
Effective Java Item 47: Know and use your libraries - Flawed random integer method example
In the example Josh gives of the flawed random method that generates a positive random number with a given upper bound n, I don't understand the two of the flaws he states.
The method from the book ...
- 313
17
votes
5
answers
11k
views
Generate random numbers distributed by Zipf
The Zipf probability distribution is often used to model file size distribution or item access distributions on items in P2P systems. e.g. "Web Caching and Zip like Distribution Evidence and ...
- 35.1k
15
votes
3
answers
8k
views
Fast weighted random selection from very large set of values
I'm currently working on a problem that requires the random selection of an element from a set. Each of the elements has a weight(selection probability) associated with it.
My problem is that for ...
user760162
13
votes
6
answers
17k
views
How to choose keys from a python dictionary based on weighted probability? [duplicate]
I have a Python dictionary where keys represent some item and values represent some (normalized) weighting for said item. For example:
d = {'a': 0.0625, 'c': 0.625, 'b': 0.3125}
# Note that sum([v ...
- 13k
13
votes
4
answers
18k
views
Chance of winning PHP percent calculation
I have a "battle" system, the attacker has a battle strength of e.g. 100, the defender has a strength of e.g. 75.
But I'm stuck now, I can't figure out how to find the winner.
I know the attacker has ...
- 177
13
votes
3
answers
22k
views
c# probability and random numbers
I want to trigger an event with a probability of 25% based on a random number generated between 1 and 100 using:
int rand = random.Next(1,100);
Will the following achieve this?
if (rand<=25)
{
...
- 479
13
votes
2
answers
5k
views
Get true or false with a given probability
I'm trying to write a function in c++ that will return true or false based on a probability given. So, for example if the probability given was 0.634 then, 63.4% of the time the function would return ...
- 301
12
votes
1
answer
2k
views
Arc4random modulo biased
According to this documentation,
arc4random_uniform() is recommended over constructions like arc4random() % upper_bound as it avoids "modulo bias" when the upper bound is not a power of two.
How ...
- 1,124
12
votes
7
answers
9k
views
How to implement Random(a,b) with only Random(0,1)? [duplicate]
Possible Duplicate:
how to get uniformed random between a, b by a known uniformed random function RANDOM(0,1)
In the book of Introduction to algorithms, there is an excise:
Describe an ...
- 25.6k
12
votes
8
answers
2k
views
What is O value for naive random selection from finite set?
This question on getting random values from a finite set got me thinking...
It's fairly common for people to want to retrieve X unique values from a set of Y values. For example, I may want to ...
- 12.6k
12
votes
6
answers
4k
views
How to generate correlated binary variables
I need to generate a series of N random binary variables with a given correlation function. Let x = {xi} be a series of binary variables (taking the value 0 or 1, i running from 1 to N). The marginal ...
- 935
11
votes
3
answers
14k
views
Probability of getting the same value using Math.random
The requirement is to send a unique id to database when user click on submit button. So I am using Javascript Math.random method. I just want to know what are the chances or possibility to get same ...
- 7,761
11
votes
2
answers
5k
views
Uniform distribution from a fractal Perlin noise function in C#
My Perlin noise function (which adds up 6 octaves of 3D simplex at 0.75 persistence) generates a 2D array array of doubles.
These numbers each come out normalized to [-1, 1], with mean at 0. I clamp ...
- 26k
10
votes
4
answers
55k
views
Random numbers with different probabilities [duplicate]
I need to randomly determine a yes or no outcome (kind of a coin flip) based on a probability that I can define (.25, .50, .75).
So for example, I want to randomly determine yes or no where yes has a ...
- 2,202
10
votes
4
answers
9k
views
Generate Random Numbers with Probabilistic Distribution
Ok, so here's my problem. We are looking at purchasing a data set from a company to augment our existing data set. For the purposes of this question, let's say that this data set ranks places with ...
- 164k
10
votes
3
answers
8k
views
Generate a uniformly random point within an annulus (ring) [duplicate]
Possible Duplicate:
Create random number within an annulus
I would like to obtain a uniformly obtained random point within an annulus, that is, the area that lies inside a circle of radius R1, ...
- 9,516
9
votes
3
answers
5k
views
Random numbers based on a probability
I'm having trouble generating random numbers that do not follow a discrete uniform distribution.
So for example, say I have 5 numbers (to keep it simple), a probability of number k being generated ...
- 955
9
votes
2
answers
6k
views
C++ function for picking from a list where each element has a distinct probability
I have an array of structs and one of the fields in the struct is a float. I want to pick one of the structs where the probability of picking it is relative to the value of the float. ie
struct s{
...
- 1,723
9
votes
1
answer
4k
views
How to generate a random number from specified discrete distribution?
Lets say we have some discrete distribution with finite number of possible results, is it possible to generate a random number from this distribution faster than in O(logn), where n is number possible ...
- 2,795
8
votes
3
answers
6k
views
Returning a random value from array with probability proportional to it's value
I have an array like
$keywords = array('apple'=>10,'orange'=>2,'grape'=>12);
I want to randomly pick one of the "Key" from the array. However the probability distribution should be such ...
- 6,515
8
votes
7
answers
15k
views
generate random numbers within a range with different probabilities
How can i generate a random number between A = 1 and B = 10 where each number has a different probability?
Example: number / probability
1 - 20%
2 - 20%
3 - 10%
4 - 5%
5 - 5%
...and so on.
I'...
- 33k
8
votes
1
answer
8k
views
Python - modelling probability
I have a simple problem. I need a way to make a function which generates 0s in p percent cases and 1s in all other cases. I tried doing it with random.random() like this:
p = 0.40
def generate():
...
- 1,570
8
votes
3
answers
640
views
re-using random number in reservoir sampling
It was asked in relation to another question recently: Given an unknown length list, return a random item in it by scanning it only 1 time
I know you shouldn't, I just can't put my finger on a ...
- 74.8k
8
votes
4
answers
6k
views
how to numerically sample from a joint, discrete, probability distribution function
I have a 2D "heat map" or PDF that I need to recreate by random sampling. I.E. I have a 2D probability density map showing starting locations. I need to randomly choose starting locations with the ...
- 875
7
votes
6
answers
14k
views
Is Pythons random.randint statistically random?
So I'm testing an calculating the probabilities of certain dice rolls, for a game.
The base case if that rolling one 10sided die.
I did a million samples of this, and ended up with the following ...
- 27.7k
7
votes
3
answers
9k
views
Picking a random item based on probabilities
There's a similar question, I know, but it confused me, so I thought it easier to ask in my way.
So I have an array of values, positive and negative. The higher they are, the more probability they ...
- 558
7
votes
3
answers
8k
views
Choosing n numbers with fixed sum
In some code I want to choose n random numbers in [0,1) which sum to 1.
I do so by choosing the numbers independently in [0,1) and normalizing them by dividing each one by the total sum:
numbers = [...
- 31.2k
7
votes
10
answers
11k
views
JavaScript - How to randomly sample items without replacement?
JavaScript
I've tried searching for something like this, but I am not able to find it.
It's a simple idea:
a. Take a random number between 0 to 10.
b. Let's say the random number rolled is a 3.
c....
- 91
7
votes
6
answers
5k
views
Ruby: Using rand() in code but writing tests to verify probabilities
I have some code which delivers things based on weighted random. Things with more weight are more likely to be randomly chosen. Now being a good rubyist I of couse want to cover all this code with ...
- 183k
7
votes
3
answers
8k
views
How to properly sample truncated distributions?
I am trying to learn how to sample truncated distributions. To begin with I decided to try a simple example I found here example
I didn't really understand the division by the CDF, therefore I ...
- 798