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alesmenzel/pick-random-element-based-on-probability.js

Last active July 25, 2025 05:22
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Select random element from array by probability
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pick-random-element-based-on-probability.js
const arr = ['A', 'B', 'C'];
// Probability map
const weight = {
A: 0.5,
B: 0.3,
C: 0.2
};
const find = input =>
arr.find((el, i) => {
const sum = arr.slice(0, i + 1).reduce((acc, el) => {
return acc + weight[el];
}, 0);
if (input < sum) {
return true;
}
return false;
});
console.log(find(0.45)); // A <0, 0.5)
console.log(find(0.6)); // B <0.5, 0.8)
console.log(find(0.85)); // C <0.8, 1) - 1 is exclusive, same as Math.random()
console.log(find(Math.random())); // Random
@TheTridentGuy
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TheTridentGuy commented Jul 23, 2022 •
edited
Loading

This seems to work:

var li = {'A': 0, 'B':0, 'C':0}
for(i=0; i<1000; i++){
    li[find(Math.random())] += 1
}

-> {A: 518, B: 287, C: 195}

Thx for the code, just what i needed!

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