generating random numbers with different probabilities

Question

Is possible to generate random numbers in PHP, for example from 1 to 10, and let it be more likely to generate smaller numbers than higher numbers?

You need to define a distribution function for your random numbers. Having this function you can code your custom random generator. — hek2mgl, Apr 30 '14 at 08:09
No rand(1,10) generate number from 1 to 10 with same probability to get each, I want it to be more probable to generate 1,2,3.. than 7,8,9. — MrDi, Apr 30 '14 at 08:10
Or a quick and dirty probability shift: `echo (rand(1,12)%10);` resulting in a non-uniform distribution as 0 and 1 have now a much higher probability. — Samuel, Apr 30 '14 at 08:10
From a very old question - [generate random numbers with probabilistic distribution](http://stackoverflow.com/questions/3109670/generate-random-numbers-with-probabilistic-distribution/3109793#3109793) — Mark Baker, Apr 30 '14 at 08:15
The first comment gives the correct solution to the problem, but the OP clearly does not understand it. Perhaps he should try harder. — Philip Sheard, Apr 30 '14 at 08:19

score 4 · Answer 1 · answered Apr 30 '14 at 08:10

Sure. Just do more randomness:

//80% chance that it's going to be a number that's smaller or equal to 5
if (rand(0, 10) <= 8) { 
    $number = rand(0, 5);
} else {
    $number = rand(6, 10);
}

Demo code:

<?php

$numbers = array();

for ($i = 0; $i < 1000; $i++) {
    if (rand(0, 10) <= 8) { 
        $number = rand(0, 5);
    } else {
        $number = rand(6, 10);
    }

    $numbers[$number] = (isset($numbers[$number]) ? $numbers[$number] + 1 : 1);
}

print_r($numbers);

Output:

Array
(
    [0] => 141
    [1] => 147
    [2] => 135
    [3] => 137
    [4] => 131
    [5] => 148
    [6] => 34
    [7] => 27
    [8] => 36
    [9] => 33
    [10] => 31
)

DEMO

generating random numbers with different probabilities

1 Answers1