I am creating a new matrix where I want to take the rows of the original matrix and make them into columns as well as take the columns of the original matrix and make them into rows.

so a matrix of :

[[1,2] [3,4] [[1,3,5] [5,6]] turns into [2,4,6]]

When I initialize the new matrix while using the fill() method to create my rows, the insertions duplicate for every row when inserting into a row.

const arrOne = [[1,2,3],[4,5,6],[7,8,9]] var transpose = function(matrix) { const transposedArr = new Array(matrix[0].length).fill(new Array()); // initializes array to [ [], [], [] ] //iterate through row for(let i = 0; i < matrix.length; i++) { //iterate through columns at row for(let j = 0; j < matrix[i].length; j++) { transposedArr[j].push(matrix[i][j]) } } return transposedArr; }; console.log(transpose(arrOne));

This will print

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

when I initialize my array using a for loop, I do not get duplicate entries

const arrOne = [[1,2,3],[4,5,6],[7,8,9]] var transpose = function(matrix) { const transposedArr = [] // initializing using const transposedArr = Array() also works! for(let i = 0; i < matrix[0].length; i++) { // initializes array to [ [], [], [] ] transposedArr.push(new Array()) } //iterate through row for(let i = 0; i < matrix.length; i++) { //iterate through columns at row for(let j = 0; j < matrix[i].length; j++) { transposedArr[j].push(matrix[i][j]) } } return transposedArr; }; console.log(transpose(arrOne));

This will print

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

**ASK**: Why is it that when I initialize the array using the fill() method, it is duplicating my insertions for each row?

I came across this issue when working on this Leetcode problem: https://leetcode.com/problems/transpose-matrix/

I also tested this code in repl.it to make sure it wasn’t an issue in Leetcode’s environment.

## Answer

const matrix = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]; /* Allocate newMatrix array */ const newMatrix = []; for (const i in matrix) { const temp = []; for (const j in matrix[i]) temp.push(matrix[j][i]); newMatrix.push(temp); } console.log(newMatrix);

First of all, I have created and new array with the opposite length from the **first array** `(Rows = Cols / Cols = Rows)`

.

Then you just have to initialize the **second array** with `[i][j] = [j][i]`

so it will initialize the column of the original matrix to the row of the new one.

Hope you understood.

By the way fill method “fills” the array element to a STATIC value, and the parameters should be (value, start, end).

Documentation: Array.prototype.fill()