CODEWITHSUNDEEP
phpmathrandom
Liad Livnat
Liad Livnat

Reputation: 7475

PHP array of probability with fractions

i have the following array:

public $percentage = array(
   0 => 20.30,
   1=> 19.96,
   2=> 14.15,
   3=> 45.59
);

// it sums in 100%

I need a random function to return the key by the percentage of the value,

for example: the possibility to get 0 is 20.30% and the possibility to get 2 is 14.15%, the first user got 0, the second one got 2.

Please let me know what is the function you suggest me to use.

Upvotes: 4

Views: 857

Answers (4)

Antony
Antony

Reputation: 15106

Convert the percentages to an accumulated probability, then compare it with a random number.

If the random number falls into a category, outputs the result. If not, move onto the next one until one is found. This allows you to output a number based on the percentage probability stated in the array.

$percentage = array(
   0 => 20.30,
   1=> 19.96,
   2=> 14.15,
   3=> 45.59
);
$random = mt_rand(0,10000)/100;
foreach ($percentage as $key => $value) {
    $accumulate += $value;
    if ($random <= $accumulate) {
        echo $key;
        break;
    }
}

Upvotes: 7

saada
saada

Reputation: 2761

$random_n = mt_rand(0,10000)/100;
while(true){
  if($random_n <= $percentage[0])
    echo 0; break;
  else if($random_n <= $percentage[1])
    echo 1; break;
  else if($random_n <= $percentage[2])
    echo 2; break;
  else if($random_n <= $percentage[3])
    echo 3; break;
  else
    $random_n = mt_rand(0,10000)/100; //generate a new random #
}

Upvotes: 2

Alexey
Alexey

Reputation: 3484

<?php
$percentage = $tmp = array(
   0 => 20.30,
   1=> 19.96,
   2=> 14.15,
   3=> 45.59
);

sort($tmp);

$rand = mt_rand(0,100);
foreach($tmp as $percent) {
    if($percent >= $rand) {
        echo array_search($percent,$percentage);
        die();
    }
}

echo (count($percentage) - 1);

Upvotes: 1

jbr
jbr

Reputation: 6258

I'd do something like:

  1. Take a random number between 1 and 10000 (because you have four significant digits)
  2. If the number is between 1 and 2030 then it's a zero, if it's between 2031 and (2031+1996) then it's a 1 etc.
  3. ...
  4. Profit

Upvotes: 0

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