/** * This is the internal implementation of quantiles: when you know * that the order is sorted, you don't need to re-sort it, and the computations * are faster. * * @param {number[]} x sample of one or more data points * @param {number} p desired quantile: a number between 0 to 1, inclusive * @returns {number} quantile value * @throws {Error} if p is outside of the range from 0 to 1 * @throws {Error} if x is empty * @example * quantileSorted([3, 6, 7, 8, 8, 9, 10, 13, 15, 16, 20], 0.5); // => 9 */export function quantileSorted(x: number[], p: number): number { const idx = x.length * p; if (!x.length) { throw new Error("quantile requires at least one data point."); } else if (p < 0 || p > 1) { throw new Error("quantiles must be between 0 and 1"); } else if (p === 1) { // If p is 1, directly return the last element return x[x.length - 1]; } else if (p === 0) { // If p is 0, directly return the first element return x[0]; } else if (idx % 1 !== 0) { // If p is not integer, return the next element in array return x[Math.ceil(idx) - 1]; } else if (x.length % 2 === 0) { // If the list has even-length, we'll take the average of this number // and the next value, if there is one return (x[idx - 1] + x[idx]) / 2; } else { // Finally, in the simple case of an integer value // with an odd-length list, return the x value at the index. return x[idx]; }}