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30-seconds-of-code/snippets/percentile.md
2017-12-17 17:55:51 +02:00

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### percentile
Uses the percentile formula to calculate how many numbers in the given array are less or equal to the given value.
Use `Array.reduce()` to calculate how many numbers are below the value and how many are the same value and apply the percentile formula.
```js
const percentile = (arr, val) =>
100 * arr.reduce((acc,v) => acc + (v < val ? 1 : 0) + (v === val ? 0.5 : 0), 0) / arr.length;
// percentile([1,2,3,4,5,6,7,8,9,10], 6) -> 55
```