percentile.js

/**
 * Gets the index of the element in an array that corresponds to the given percentile
 * @param {number} arrLength the length of the array that we want to calculate its percentile
 * @param {number} p the percentile in the range [0..100] inclusive
 * @returns index of the array element that corresponds to the given percentile
 */
export function percentileIndex(arrLength, p) {
    const maxPossibleIndex = arrLength - 1
    return Math.ceil(maxPossibleIndex * p / 100)
}

/**
 * @returns the value at the nth location in the array where n is between 0 to array.length
 */
export function percentile(arr, p) {
    return arr[percentileIndex(arr.length)]
}