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TypeScript - random values from array with probability (different probability per item)
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In this short article, we would like to show how in TypeScript, get random items from an array using different randomization probabilities per item.
The main idea used in the below example to randomize items with different probabilities is to create an array that represents items distribution - items are repeated many times to affect randomization.
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const createDistribution = (array: string[], weights: number[], size: number): string[] => {2
const distribution = [];3
const sum = weights.reduce((a, b) => a + b);4
const quant = size / sum;5
for (let i = 0; i < array.length; ++i) {6
const limit = quant * weights[i];7
for (let j = 0; j < limit; ++j) {8
distribution.push(i);9
}10
}11
return distribution;12
};13
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const randomIndex = (distribution: string[]): string => {15
const index = Math.floor(distribution.length * Math.random()); // random index16
return distribution[index];17
};18
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// Usage example:21
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const array: string[] = ['John', 'Chris', 'Ann']; // used values in radomization23
const weights: number[] = [0.5, 0.2, 0.3]; // specific items probability (5 + 2 + 3 = 10)24
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const distribution: string[] = createDistribution(array, weights, 10); // 10 - describes distribution array size (it affects on precision)26
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for (let i = 0; i < 10; ++i) {28
const index = randomIndex(distribution);29
console.log(array[index]); // random value located in the array30
}Example output:
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John2
Chris3
Ann4
Chris5
Chris6
Ann7
John8
John9
Ann10
John