@numio/bigmath/src/quartile/utils.js

@numio/bigmath is an arbitrary-precision arithmetic library. It can be used for basic operations with decimal numbers (integers and float)

import { PipeInner } from "../pipe/utils.js";
const meanQ = (idx, array) => {
    const { bi: left } = new PipeInner().add([array[idx], array[idx - 1]]);
    return new PipeInner().div([left, [2n, 0]]).bi;
};
export const quartileInner = (array) => {
    if (array.length < 3) {
        throw Error("To calculate quartile you need at least 3 elements");
    }
    const { length } = array;
    const Q2Idx = length >> 1;
    const Q1Idx = Q2Idx >> 1;
    const Q3Idx = length - Q1Idx;
    const isEvenHalf = Q2Idx % 2 !== 0;
    return {
        Q1: isEvenHalf ? array[Q1Idx] : meanQ(Q1Idx, array),
        Q2: length % 2 !== 0 ? array[Q2Idx] : meanQ(Q2Idx, array),
        Q3: isEvenHalf ? array[Q3Idx - 1] : meanQ(Q3Idx, array),
    };
};