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Weighted probability random choice array

I have an array and returning random values.

const array = [ 1, 2 ,3 ,4 ,5, 6, 7, 8]
const rand = array[~~(Math.random() * array.length)]

I would like to return a random element of the array, but with a weighted probability that higher indexes (indices) are less likely to be returned. i.e 8 is less likely to be returned than 1.

How can I achieve this?.

Solution

  • You can use a trick that clones the origin array to a new array by weighted probability.

    You can modify it by:

    • increase weight on which item you want to show more
    • decrease weight on which item you want to show less.

    You can check the below demo:

    const array = [ 1, 2 ,3 ,4 ,5, 6, 7, 8 ]
const weight = [ 8, 7, 6, 5, 4, 3, 2, 1 ];

let randomArray = [];
array.forEach((item, index) => {
   var clone = Array(weight[index]).fill(item);
   randomArray.push(...clone);
});

const result = randomArray[~~(Math.random() * randomArray.length)]

console.log('random value:', result);