27 lines
821 B
Markdown
27 lines
821 B
Markdown
---
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title: weightedSample
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tags: array,random,advanced
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---
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Returns a random element from an array, using the provided `weights` as the probabilities for each element.
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Use `Array.prototype.reduce()` to create an array of partial sums for each value in `weights`.
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Use `Math.random()` to generate a random number and `Array.prototype.findIndex()` to find the correct index based on the array previously produced.
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Finally, return the element of `arr` with the produced index.
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```js
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const weightedSample = (arr, weights) => {
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let roll = Math.random();
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return arr[
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weights
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.reduce((acc, w, i) => (i === 0 ? [w] : [...acc, acc[acc.length - 1] + w]), [])
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.findIndex((v, i, s) => roll >= (i === 0 ? 0 : s[i - 1]) && roll < v)
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];
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};
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```
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```js
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weightedSample([3, 7, 9, 11], [0.1, 0.2, 0.6, 0.1]); // 9
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```
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