Transpose of a two-dimensional array - JavaScript

The transpose of a matrix (2-D array) is simply a flipped version of the original matrix. We can transpose a matrix by switching its rows with its columns.

For example, if we have a 3×3 matrix where the first row is [1, 1, 1], after transposing, the first column becomes [1, 1, 1].

Understanding Matrix Transpose

Let's visualize how transposition works with a simple example:

Original Matrix:
[1, 1, 1]
[2, 2, 2] 
[3, 3, 3]

Transposed Matrix:
[1, 2, 3]
[1, 2, 3]
[1, 2, 3]

Method 1: In-Place Transpose (Modifies Original)

This approach modifies the original array by swapping elements:

const arr = [
    [1, 1, 1],
    [2, 2, 2],
    [3, 3, 3]
];

const transpose = arr => {
    for (let i = 0; i 

Original: [[1,1,1],[2,2,2],[3,3,3]]
Transposed: [[1,2,3],[1,2,3],[1,2,3]]


Method 2: Creating New Transposed Array

This approach creates a new array without modifying the original:

const arr = [
    [1, 1, 1],
    [2, 2, 2],
    [3, 3, 3]
];

const transposeNew = matrix => {
    return matrix[0].map((col, i) => matrix.map(row => row[i]));
};

const original = JSON.stringify(arr);
const transposed = transposeNew(arr);

console.log("Original:", original);
console.log("Transposed:", JSON.stringify(transposed));
console.log("Original unchanged:", JSON.stringify(arr));


Original: [[1,1,1],[2,2,2],[3,3,3]]
Transposed: [[1,2,3],[1,2,3],[1,2,3]]
Original unchanged: [[1,1,1],[2,2,2],[3,3,3]]


Method 3: Using Traditional For Loops

const arr = [
    [1, 4, 7],
    [2, 5, 8],
    [3, 6, 9]
];

const transposeTraditional = matrix => {
    const rows = matrix.length;
    const cols = matrix[0].length;
    const result = [];
    
    for (let i = 0; i 

Original: [[1,4,7],[2,5,8],[3,6,9]]
Transposed: [[1,2,3],[4,5,6],[7,8,9]]


Comparison

Conclusion

Use in-place transposition for memory efficiency when you don't need the original matrix. For preserving the original data, the map() method offers cleaner, more functional code.