in javascript, how do you sort a subset of an array?

Question

I have an array and would like to sort all but the last n elements.

For example, if the array is 10 elements long, would like elements 0 through 7 to be sorted while ele

Answer 1

An ES6 riff on the solution provided by @darin

let subSort = (arr, i, n, sortFx) => [].concat(...arr.slice(0, i), ...arr.slice(i, i + n).sort(sortFx), ...arr.slice(i + n, arr.length));

• i is the index where the subsection begins
• n is the number of elements to sort
• sortFx is the sorting function

So it's possible to sort a range within an array:

var array = [5, 2, 6, 4, 1, 9, 3, 8, 7];
// sort array beginning at index 2; sort 4 elements of array
subSort(array, 2, 4, (a, b) => a - b);
// array is now [5, 2, 1, 4, 6, 9, 3, 8, 7]
subSort(array, 2, 4, (a, b) => b - a);
// array is now [5, 2, 9, 6, 4, 1, 3, 8, 7]

subSort() can be used for objects of arbitrary complexity.

Answer 2

var array = [5, 2, 6, 4, 1, 9, 3, 8, 7];
array = array.slice(0, 7).sort().concat(array.slice(7, 10));
// array is now [1, 2, 3, 4, 5, 6, 9, 8, 7]

Answer 3

If you need to sort the array in place (i.e. without creating a new, sorted array), which is what the sort() method does, you could do the following:

var array = [5, 2, 6, 4, 0, 1, 9, 3, 8, 7];
var unsorted = array.slice(7);
array.length = 7;
array.sort().push.apply(array, unsorted);

More generally, here's a function to sort a portion of an array in place. Like the sort() method, it also returns a reference to the array.

function partialSort(arr, start, end) {
    var preSorted = arr.slice(0, start), postSorted = arr.slice(end);
    var sorted = arr.slice(start, end).sort();
    arr.length = 0;
    arr.push.apply(arr, preSorted.concat(sorted).concat(postSorted));
    return arr;
}

Example:

var array = [5, 2, 6, 4, 0, 1, 9, 3, 8, 7];
partialSort(array, 0, 7);