Swap rows with columns (transposition) of a matrix in javascript [duplicate]
DuckDucking turned up this by Ken. Surprisingly, it's even more concise and complete than Nikita's answer. It retrieves column and row lengths implicitly within the guts of map().
function transpose(a) { return Object.keys(a[0]).map(function(c) { return a.map(function(r) { return r[c]; }); });}console.log(transpose([ [1,2,3], [4,5,6], [7,8,9]]));![[[1,4,5],[2,5,8],[7,8,9]](https://i.stack.imgur.com/VsPQn.png)
See article: Transpose An Array In JavaScript and jQuery
function transpose(a) { // Calculate the width and height of the Array var w = a.length || 0; var h = a[0] instanceof Array ? a[0].length : 0; // In case it is a zero matrix, no transpose routine needed. if(h === 0 || w === 0) { return []; } /** * @var {Number} i Counter * @var {Number} j Counter * @var {Array} t Transposed data is stored in this array. */ var i, j, t = []; // Loop through every item in the outer array (height) for(i=0; i<h; i++) { // Insert a new row (array) t[i] = []; // Loop through every item per item in outer array (width) for(j=0; j<w; j++) { // Save transposed data. t[i][j] = a[j][i]; } } return t;}console.log(transpose([[1,2,3],[4,5,6],[7,8,9]]));
Just like in any other language:
int[][] copy = new int[columns][rows];for (int i = 0; i < rows; ++i) { for (int j = 0; j < columns; ++j) { copy[j][i] = original[i][j]; }}You just have to construct the 2D array differently in JS. Like this:
function transpose(original) { var copy = []; for (var i = 0; i < original.length; ++i) { for (var j = 0; j < original[i].length; ++j) { // skip undefined values to preserve sparse array if (original[i][j] === undefined) continue; // create row if it doesn't exist yet if (copy[j] === undefined) copy[j] = []; // swap the x and y coords for the copy copy[j][i] = original[i][j]; } } return copy;}console.log(transpose([ [1,2,3], [4,5,6], [7,8,9]]));