Generate random numbers with weighted probabilites [duplicate]

问题

I want to select a number randomly, but based on probability from a group of numbers; for example (2-6).

I'd like the following distribution:

6's probability should be 10%
5's probability should be 40%
4's probability should be 35%
3's probability should be 5%
2's probability should be 5%

回答1:

The best you can do is generate a number between 0 and 100, and see in what range the number is:

$num=rand(0,100);

if ($num<10+40+35+5+5) 
    $result=2;

if ($num<10+40+35+5)
    $result=3;

if ($num<10+40+35)
    $result=4;

if ($num<10+40)
    $result=5;

if ($num<10)
    $result=6;

Be careful, your total probability isn't equal to 1, so sometimes $result is undefined

See @grigore-turbodisel 's answer if you want something that you can configure easily.

回答2:

This is very easy to do. Watch for the comments in the code below.

$priorities = array(
    6=> 10,
    5=> 40,
    4=> 35,
    3=> 5,
    2=> 5
);

# you put each of the values N times, based on N being the probability
# each occurrence of the number in the array is a chance it will get picked up
# same is with lotteries
$numbers = array();
foreach($priorities as $k=>$v){
    for($i=0; $i<$v; $i++)  
        $numbers[] = $k;
}

# then you just pick a random value from the array
# the more occurrences, the more chances, and the occurrences are based on "priority"
$entry = $numbers[array_rand($numbers)];
echo "x: ".$entry;

回答3:

Create a number between 1 and 100.

If      it's <= 10       -> 6
Else if it's <= 10+40    -> 5
Else if it's <= 10+40+35 -> 4

And so on...

Note: your probabilities don't add up to 100%.

来源：https://stackoverflow.com/questions/17614638/generate-random-numbers-with-weighted-probabilites

标签

php

algorithm

random