quickselect

A tiny and fast selection algorithm in JavaScript
(specifically, Floyd-Rivest selection).

 quickselect(array, k[, left, right, compareFn]);

Rearranges items so that all items in the [left, k] are the smallest.
The k-th element will have the (k - left + 1)-th smallest value in [left, right].

• array: the array to partially sort (in place)
• k: middle index for partial sorting (as defined above)
• left: left index of the range to sort (0 by default)
• right: right index (last index of the array by default)
• compareFn: compare function

Example:

 var arr = [65, 28, 59, 33, 21, 56, 22, 95, 50, 12, 90, 53, 28, 77, 39];

quickselect(arr, 8);

// arr is [39, 28, 28, 33, 21, 12, 22, 50, 53, 56, 59, 65, 90, 77, 95]
//                                         ^^ middle index