Transposing a 2D-array in JavaScript

javascript arrays transpose matrix

2022-08-30 00:59:59

I've got an array of arrays, something like:

[
    [1,2,3],
    [1,2,3],
    [1,2,3],
]

I would like to transpose it to get the following array:

[
    [1,1,1],
    [2,2,2],
    [3,3,3],
]

It's not difficult to programmatically do so using loops:

function transposeArray(array, arrayLength){
    var newArray = [];
    for(var i = 0; i < array.length; i++){
        newArray.push([]);
    };

    for(var i = 0; i < array.length; i++){
        for(var j = 0; j < arrayLength; j++){
            newArray[j].push(array[i][j]);
        };
    };

    return newArray;
}

This, however, seems bulky, and I feel like there should be an easier way to do it. Is there?

答案 1

output = array[0].map((_, colIndex) => array.map(row => row[colIndex]));

map calls a provided function once for each element in an array, in order, and constructs a new array from the results. is invoked only for indexes of the array which have assigned values; it is not invoked for indexes which have been deleted or which have never been assigned values.callbackcallback

callback is invoked with three arguments: the value of the element, the index of the element, and the Array object being traversed. [source]

答案 2

Many good answers here! I consolidated them into one answer and updated some of the code for a more modern syntax:

One-liners inspired by Fawad Ghafoor and Óscar Gómez Alcañiz

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

function transpose(matrix) {
  return matrix[0].map((col, c) => matrix.map((row, r) => matrix[r][c]));
}

Functional approach style with reduce by Andrew Tatomyr

function transpose(matrix) {
  return matrix.reduce((prev, next) => next.map((item, i) =>
    (prev[i] || []).concat(next[i])
  ), []);
}

Lodash/Underscore by marcel

function tranpose(matrix) {
  return _.zip(...matrix);
}

// Without spread operator.
function transpose(matrix) {
  return _.zip.apply(_, [[1,2,3], [1,2,3], [1,2,3]])
}

Even simpler Lodash/Underscore solution by Vigrant

_.unzip(matrix);

Vanilla approach

function transpose(matrix) {
  const rows = matrix.length, cols = matrix[0].length;
  const grid = [];
  for (let j = 0; j < cols; j++) {
    grid[j] = Array(rows);
  }
  for (let i = 0; i < rows; i++) {
    for (let j = 0; j < cols; j++) {
      grid[j][i] = matrix[i][j];
    }
  }
  return grid;
}

Vanilla in-place ES6 approach inspired by Emanuel Saringan

function transpose(matrix) {
  for (var i = 0; i < matrix.length; i++) {
    for (var j = 0; j < i; j++) {
      const temp = matrix[i][j];
      matrix[i][j] = matrix[j][i];
      matrix[j][i] = temp;
    }
  }
}

// Using destructing
function transpose(matrix) {
  for (var i = 0; i < matrix.length; i++) {
    for (var j = 0; j < i; j++) {
      [matrix[i][j], matrix[j][i]] = [matrix[j][i], matrix[i][j]];
    }
  }
}