[removed] Sort array and return an array of indicies that indicates the position of the sorted elements with respect to the original elements

Question

Suppose I have a Javascript array, like so:

var test = [\'b\', \'c\', \'d\', \'a\'];

I want to sort the array. Obviously, I can just do th

Answer 1

This is a more idiomatic ES6 version of clerbois' answer, see his/hers for comments:

return test.map((val, ind) => {return {ind, val}})
           .sort((a, b) => {return a.val > b.val ? 1 : a.val == b.val ? 0 : -1 })
           .map((obj) => obj.ind);

Answer 2

var test = ['b', 'c', 'd', 'a'];
var test_with_index = [];
for (var i in test) {
    test_with_index.push([test[i], i]);
}
test_with_index.sort(function(left, right) {
  return left[0] < right[0] ? -1 : 1;
});
var indexes = [];
test = [];
for (var j in test_with_index) {
    test.push(test_with_index[j][0]);
    indexes.push(test_with_index[j][1]);
}

Edit

You guys are right about for .. in. That will break if anybody munges the array prototype, which I observe annoyingly often. Here it is with that fixed, and wrapped up in a more usable function.

function sortWithIndeces(toSort) {
  for (var i = 0; i < toSort.length; i++) {
    toSort[i] = [toSort[i], i];
  }
  toSort.sort(function(left, right) {
    return left[0] < right[0] ? -1 : 1;
  });
  toSort.sortIndices = [];
  for (var j = 0; j < toSort.length; j++) {
    toSort.sortIndices.push(toSort[j][1]);
    toSort[j] = toSort[j][0];
  }
  return toSort;
}

var test = ['b', 'c', 'd', 'a'];
sortWithIndeces(test);
alert(test.sortIndices.join(","));

Answer 3

You can do this with the Map object. Just set the key/value as index/value and use the Array.from to get the Iterator as a bi-dimensional array then sort either the indexes, the values or both.

function sorting(elements) {
  const myMap = new Map();
  elements.forEach((value, index) => {
    myMap.set(index, value);
  });
  const arrayWithOrderedIndexes = Array.from(myMap.entries()).sort((left, right) => {return left[1] < right[1] ? -1 : 1});
  myMap.clear();
  return arrayWithOrderedIndexes.map(elem => elem[0]);
}
const elements = ['value','some value','a value','zikas value','another value','something value','xtra value'];
sorting(elements);

Answer 4

I would just fill an array with numbers 0..n-1, and sort that with a compare function.

var test = ['b', 'c', 'd', 'a'];
var len = test.length;
var indices = new Array(len);
for (var i = 0; i < len; ++i) indices[i] = i;
indices.sort(function (a, b) { return test[a] < test[b] ? -1 : test[a] > test[b] ? 1 : 0; });
console.log(indices);

Answer 5

Array.prototype.sortIndices = function (func) {
    var i = j = this.length,
        that = this;

    while (i--) {
        this[i] = { k: i, v: this[i] };
    }

    this.sort(function (a, b) {
        return func ? func.call(that, a.v, b.v) : 
                      a.v < b.v ? -1 : a.v > b.v ? 1 : 0;
    });

    while (j--) {
        this[j] = this[j].k;
    }
}

YMMV on how you feel about adding functions to the Array prototype and mutating arrays inline, but this allows sorting of an array of any objects that can be compared. It takes an optional function that can be used for sorting, much like Array.prototype.sort.

An example,

var test = [{b:2},{b:3},{b:4},{b:1}];

test.sortIndices(function(a,b) { return a.b - b.b; });

console.log(test); // returns [3,0,1,2]

Answer 6

You can accomplish this with a single line using es6 (generating a 0->N-1 index array and sorting it based on the input values).

var test = ['b', 'c', 'd', 'a']

var result = Array.from(Array(test.length).keys())
                  .sort((a, b) => test[a] < test[b] ? -1 : (test[b] < test[a]) | 0)