mat.transpose()

zip array of rows into array of columns.

👥 相關

• *zip() is like the transpose of a matrix.

💾 程式

⭐️ 注意：原矩陣各列的長度可以不一樣，但經過 transpose() 後「各行」(也就是新矩陣的各列)長度都一樣，只是可能有些元素會是 undefined❗️

• replit ⟩ zip(arrays)

/**
 * see the matrix in "columns".
 * @example
 * let m = [[1,2], [3], [5,6]];
 * m.transpose();    // [[1,3,5], [2,undefined,6]]
 * @return {[[*]]} array of "columns"
 */
const matrix_transpose = {
    /**
     * see the matrix in "columns".
     * - Note: may contain `undefined` elements if row lengths are different
     * @example
     * let m = [[1,2], [3], [5,6]];
     * m.transpose();    // [[1,3,5], [2,undefined,6]]
     * @return {[[*]]} array of "columns"
     */
    transpose() {
        return Array.from(
            { length: Math.max(...this.map(row => row.length)) }, // number of columns
            (_, j) => this.map(row => row[j])   // for each row, choose jth column
        )
    }
};

export default matrix_transpose;

💈範例：

import matrix_transpose from '/.../matrix_transpose.mjs';
Object.assign(Array.prototype, matrix_transpose);

let m1 = [[1, 2], [3, 4], [5, 6]];
// 1 2
// ---                    1 | 2
// 3 4  --(transpose)-->  3 | 4  (see matrix in "columns")
// ---                    5 | 6
// 5 6

let m2 = [[1, 2], [3], [5, 6]];
m1.transpose() // [[1,3,5], [2,4,6]]
m2.transpose() // [[1,3,5], [2,undefined,6]]

⬇️ 應用

• mat.maxElementInEachColumn()

📗 參考

• QuickRef ⟩ How to zip multiple arrays in JavaScript
• GitHub ⟩ versatile JavaScript "zip" function

📘 手冊

• Array.from()

🗣 討論

• How do I zip two arrays in JavaScript?
• Transposing a 2D-array in JavaScript