# Percentile of matches

JavaScript, Math · Oct 22, 2020

Calculates the percentage of numbers in the given array that are less or equal to the given value.

- Use
`Array.prototype.reduce()`

to calculate how many numbers are below the value and how many are the same value and apply the percentile formula.

```
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`