locutus/haskell/list/transpose.js

Locutus other languages' standard libraries to JavaScript for fun and educational purposes

"use strict";
Object.defineProperty(exports, "__esModule", { value: true });
exports.transpose = transpose;
function transpose(rows) {
    //  discuss at: https://locutus.io/haskell/list/transpose/
    // original by: Kevin van Zonneveld (https://kvz.io)
    //      note 1: Transposes rows and columns, dropping exhausted rows like Haskell Data.List.transpose.
    //   example 1: transpose([[1, 2, 3], [4, 5, 6]])
    //   returns 1: [[1, 4], [2, 5], [3, 6]]
    //   example 2: transpose([['a', 'b'], ['c'], ['d', 'e', 'f']])
    //   returns 2: [['a', 'c', 'd'], ['b', 'e'], ['f']]
    //   example 3: transpose([])
    //   returns 3: []
    if (!Array.isArray(rows)) {
        return [];
    }
    const queue = rows
        .filter((row) => Array.isArray(row))
        .map((row) => row.slice())
        .filter((row) => row.length > 0);
    const out = [];
    while (queue.length > 0) {
        const column = [];
        for (let i = queue.length - 1; i >= 0; i--) {
            const row = queue[i];
            const head = row?.shift();
            if (typeof head !== 'undefined') {
                column.push(head);
            }
            if (!row || row.length === 0) {
                queue.splice(i, 1);
            }
        }
        column.reverse();
        out.push(column);
    }
    return out;
}