Question

123

Toggle array sort in Javascript (ascending to descending and vice versa)

rated 0 times [ 124] [ 1] / answers: 1 / hits: 44019 / 12 Years ago, thu, january 24, 2013, 12:00:00

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.

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mickaylag

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3 Years ago

answered 12 Years ago deonkalvinw · Accepted Answer

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;

}