Function pdqselect::select_by

pub fn select_by<T, F>(v: &mut [T], k: usize, compare: F) where
    F: FnMut(&T, &T) -> Ordering, 

Partially sorts a slice using compare to compare elements and puts the kth smallest item in place.

This sort is in-place, unstable, and O(n log n) worst-case.

The implementation is based on Orson Peters’ pattern-defeating quickselect.

Examples

let mut v = [5, 4, 1, 3, 2];
let k = 2;
pdqselect::select_by(&mut v, k, |a, b| a.cmp(b));
assert!(v[..k].iter().all(|&x| x <= v[k]));
assert!(v[k+1..].iter().all(|&x| x >= v[k]));

// reverse sorting
pdqselect::select_by(&mut v, k, |a, b| b.cmp(a));
assert!(v[..k].iter().all(|&x| x >= v[k]));
assert!(v[k+1..].iter().all(|&x| x <= v[k]));