Re-order an array by indexes with javascript [duplicate]

Question

I have an array and I’m trying to re-order this array based on another array. The second array is an array of indexes (see below). I’m looking to build a clean function to take two arguments (an array and an array of indexes), and return the re-ordered array. I've tried to build this function and have an example below, however it's not returning what I'm expecting. Any help is greatly appreciated.

var before = ["T", "T", "A", "T", "T", "T", "T", "T", "A", "T", "T","T", "W", "W", "W", "W", "T", "T", "T", "T", "T", "W", "T"];
var indexes = [8, 2, 11, 22, 0, 4, 5, 18, 6, 17, 16, 19, 7, 3, 20, 1, 10, 9, 14, 13, 21, 12, 15];

// Attempt
function reorderArray(arrayToOrder ,order){
    // Get a copy of the array we want to change
    var temp = arrayToOrder
    // loop through the indexes
    // use the indexes to place the items in the right place from the copy into the original
    for(let i = 0; i < arrayToOrder.length; i++) {
        console.log("arr: ", arrayToOrder[order[i]] );
        console.log("temp: ", temp[i] );
        arrayToOrder[order[i]] = temp[i];
    }
    return arrayToOrder;
}
// run function
reorderArray( before, indexes );

// function should return this array
var after = ["A", "A", "T", "T", "T", "T", "T", "T", "T", "T", "T", "T", "T", "T", "T", "T", "T", "T", "W", "W", "W", "W", "W"];

Please note that copying reference of an object (arrays are also objects) doesn't create a copy. It actually create another reference to the same object. — Mohammad Usman
– Mohammad Usman, Commented Jul 12, 2018 at 18:56
Your after looks like an alpha SORT not an index of the other array list. Is this supposed to be a trick question :) — Mark Schultheiss
– Mark Schultheiss, Commented Jul 12, 2018 at 19:15
The question needs to be retitled, reworded, or corrected, The example code show how to reorder an array according to "rank", since it uses something like arrayToOrder[rank[i]] = temp[i]; . If reordering an array according to "indexes", the key line of code is arrayToOrder[i] = temp[index[i]]; . I don't know which case is more common, but one example of this is sorting an array of indexes 0 to length-1, according to another array, and in this case, the reorder is done according to indexes. You can convert indexes to rank : rank[index[i]] = i; or vice versa index[rank[i]] = i; . — rcgldr
– rcgldr, Commented Jul 13, 2018 at 20:34

Zohaib Ijaz · Accepted Answer · 2018-07-12 18:57:31Z

3

You can use Array.prototype.map

var before = ["T", "T", "A", "T", "T", "T", "T", "T", "A", "T", "T","T", "W", "W", "W", "W", "T", "T", "T", "T", "T", "W", "T"];
var indexes = [8, 2, 11, 22, 0, 4, 5, 18, 6, 17, 16, 19, 7, 3, 20, 1, 10, 9, 14, 13, 21, 12, 15];

var output = indexes.map(i => before[i]);

console.log(output);

answered Jul 12, 2018 at 18:57

Zohaib Ijaz

23k7 gold badges43 silver badges63 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

MostlyRquestions Over a year ago

Exactly what I was looking for,Thanks!

Ori Drori · Accepted Answer · 2018-07-12 18:55:37Z

1

Iterate the indexes with Array.map(), and return the value from the before array:

const before = ["T", "T", "A", "T", "T", "T", "T", "T", "A", "T", "T","T", "W", "W", "W", "W", "T", "T", "T", "T", "T", "W", "T"];
const indexes = [8, 2, 11, 22, 0, 4, 5, 18, 6, 17, 16, 19, 7, 3, 20, 1, 10, 9, 14, 13, 21, 12, 15];

const reorderByIndexes = (arr, order) => order.map((index) => arr[index]);
  
const after = reorderByIndexes(before, indexes);

console.log(after.join());

answered Jul 12, 2018 at 18:55

Ori Drori

196k32 gold badges243 silver badges233 bronze badges

Comments

Mark Schultheiss · Accepted Answer · 2018-07-12 19:21:16Z

0

Or with a forEach if you don't want to use ES6

var before = ["T", "T", "A", "T", "T", "T", "T", "T", "A", "T", "T", "T", "W", "W", "W", "W", "T", "T", "T", "T", "T", "W", "T"];
var indexes = [8, 2, 11, 22, 0, 4, 5, 18, 6, 17, 16, 19, 7, 3, 20, 1, 10, 9, 14, 13, 21, 12, 15];
var after = [];
indexes.forEach(function(value, index) {
  after[index] = before[value]
})

console.log(after)

edited Jul 12, 2018 at 19:21

Mark Schultheiss

34.3k13 gold badges75 silver badges116 bronze badges

answered Jul 12, 2018 at 19:03

IsraGab

5,1853 gold badges30 silver badges50 bronze badges

Collectives™ on Stack Overflow

Re-order an array by indexes with javascript [duplicate]

3 Answers 3

1 Comment

Comments

Comments

Linked

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

1 Comment

Comments

Comments

Linked

Related