Question

I am sorting my array like this:

array.sort((function(index) {
    return function(a, b){
        return (a[index] === b[index] ? 0 : (a[index] < b[index] ? -1 :1));
    };
})(0));

As you can see, it is sorted in ascending order.

My question is how do I toggle sorting? For example, if it is already in ascending order then how can I sort it in descending order and vice-versa?

I know to sort in descending I need to modify code like this:

array.sort((function(index) {
    return function(a, b) {
        return (a[index] === b[index] ? 0 : (a[index] < b[index] ? 1 :-1));
    };
})(0));

but I don’t know how to toggle.

Answer 1

If you know for certain that array is sorted then you can reverse the order by using a simple loop

var l = array.length;
for(i=0; i< l / 2; i++) {
   var t = array[i];
   array[i] = array[l - 1 - i];
   array[l - 1 - i] = t;
}

More simpler solution is to use reverse function (BTW, check this SO Q&A for different reversing algo and their performance)

If you don’t know the initial state of you array then I will advise associating a custom property to an array that will track the sort order. For example,

function sortArray(a, isAscending) {
  var currentSort = a["my_sort_order"];
  if (typeof currentSort != 'boolean') {
     // assume it be unsorted, use sort alogorithm
     a.sort(function(a,b) { return isAscending ? a - b : b - a; }); // assuming numerical array, modify as per your needs
  } else if (currentSort != isAscending) {
     // sorted but in different order, reverse the order
     a.reverse(); // or use for loop
  }
  // set the sort order
  a["my_sort_order"] = isAscending ? true : false;
}