Hướng dẫn transpose array javascript

Question

This one, is not only a super efficient one, but a pretty short solution.

Algorithm Time Complexity: O(n log n)

const matrix = [
   [1,1,1,1],
   [2,2,2,2],
   [3,3,3,3],
   [4,4,4,4]
];

matrix.every((r, i, a) => (
   r.every((_, j) => (
      j = a.length-j-1,
      [ r[j], a[j][i] ] = [ a[j][i], r[j] ],
      i < j-1
   )), 
   i < length-2
));

console.log(matrix);
/*
Prints:
[
   [1,2,3,4],
   [1,2,3,4],
   [1,2,3,4],
   [1,2,3,4]
]
*/

The example above will do only 6 iterations.
For bigger matrix, say 100x100 it will do 4,900 iterations, this is 51% faster than any other solution provided here.

The principle is simple, you on only iterate through the upper diagonal half of the matrix, because the diagonal line never changes and the bottom diagonal half being is switched together with the upper one, so there is no reason to iterate through it as well. This way, you save a lot of running time, especially in a large matrix.

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Given a 2D array (matrix) and the task is to get the transpose of the matrix using JavaScript.

Approach 1:

Store a 2D array into variable.
Display the 2D array (matrix) content.
Call map() method which provides a callback function single time for every element in an array, maintaining the order, and returns a new array (transpose of original array) from the results.

Example: This example uses array.map() method to get the transpose of the array.

HTML

<html>

<head>

<title>

Transpose of a 2D array

title>

head>

<body style = "text-align:center;">

<h2 style = "color:green;" >

GeeksForGeeks

h2>

<p id = "GFG_UP" style =

"font-size: 16px; font-family: sans-serif; font-weight: bold;">

p>

<button onclick = "gfg_Run()">

Click here

button>

<p id = "GFG_DOWN" style =

"color:green; font-size: 30px; font-weight: bold;">

p>

<script>

var el_up = document.getElementById("GFG_UP");

var el_down = document.getElementById("GFG_DOWN");

var array = [

[1, 1, 1],

[2, 2, 2],

[3, 3, 3],

];

el_up.innerHTML = "[ [ " + array[0] + " ] ], [ [ "


                             + array[1] + " ] ], [ [ " + array[2] + " ] ]";
            function transpose(mat) {
                for (var i = 0; i < mat.length; i++) {
                    for (var j = 0; j < i; j++) {
                        const tmp = mat[i][j];
                        mat[i][j] = mat[j][i];
                        mat[j][i] = tmp;
                    }
                }
            }
            function gfg_Run() {
                array = array[0].map((col, i) => array.map(row => row[i]));
                el_down.innerHTML = "[ [ " + array[0] + " ] ], [ [ "
                        + array[1] + " ] ], [ [ " + array[2] + " ] ]";



            }        
        script>
    body>
html>                   
Output: 
Before clicking on the button: 
 
After clicking on the button: 
 
Approach 2:  

Store a 2D array into variable.
Replace every element in the array by its mirror image with respect to diagonal of the array.
Example: This example creates a function which replaces every element by its mirror image to get the transpose of the array.  
HTML
<html>
    <head>
        <title>
            Transposing a 2D array
        title>
    head>
    <body style = "text-align:center;">
        <h2 style = "color:green;" >
            GeeksForGeeks
        h2>
        <p id = "GFG_UP" style =
            "font-size: 16px; font-family: sans-serif; font-weight: bold;">    
        p>
        <button onclick = "gfg_Run()">
            Click here
        button>
        <p id = "GFG_DOWN" style =
            "color:green; font-size: 30px; font-weight: bold;">
        p>



        <script>
            var el_up = document.getElementById("GFG_UP");
            var el_down = document.getElementById("GFG_DOWN");
            var array = [
                            [1, 1, 1],
                            [2, 2, 2],
                            [3, 3, 3],
                        ];
            el_up.innerHTML = "[ [ " + array[0] + " ] ], [ [ "
                    + array[1] + " ] ], [ [ " + array[2] + " ] ]";
            function transpose(mat) {
                for (var i = 0; i < mat.length; i++) {
                    for (var j
= 0; j < i; j++) {
                        const tmp = mat[i][j];
                        mat[i][j] = mat[j][i];
                        mat[j][i] = tmp;
                    }
                }
            }
            function gfg_Run() {
                transpose(array);
                el_down.innerHTML = "[ [ " + array[0] + " ] ], [ [ "
                        + array[1] + " ] ], [ [ " + array[2] + " ] ]";
            }        
        
    body>
html>                   
Output: 
Before
clicking on the button: 
 
After clicking on the button:

programming javascript Transpose array JavaScript 2D array JavaScript Pivot array javascript Rotate 2D array

Hướng dẫn transpose array javascript

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