jora/cjs/utils/stable-sort.cjs

JavaScript object query engine

'use strict';

const stableSortSize = isSortStable(20) ? Infinity : isSortStable(10) ? 10 : 0;

function isSortStable(n) {
    return Array.from({ length: n }, (_, idx) => ({ idx }))
        .sort((a, b) => (a.idx % 2) - (b.idx % 2))
        .every((a, idx) =>
            idx < n / 2 ? (a.idx >> 1 === idx) : Math.ceil(n / 2) + (a.idx >> 1) === idx
        );
}

function stableSort(array, cmp) {
    // check size, e.g. old v8 had stable sort only for arrays with length less or equal 10
    if (array.length <= stableSortSize) {
        return array.slice().sort(cmp);
    }

    return array
        .map((value, idx) => ({ value, idx }))
        .sort((a, b) =>
            (a.value === undefined
                ? b.value !== undefined
                : b.value === undefined
                    ? -1
                    : cmp(a.value, b.value)) || (a.idx - b.idx)
        )
        .map(item => item.value);
}

exports.stableSort = stableSort;