sortOn
lib.lists.sortOn
Docs pulled from | This Revision | about 2 hours ago
Sort a list based on the default comparison of a derived property b.
The items are returned in b-increasing order.
Performance:
The passed function f is only evaluated once per item,
unlike an unprepared sort using
f p < f q.
Laws:
sortOn f == sort (p: q: f p < f q)
Inputs
f-
1. Function argument
list-
2. Function argument
Type
sortOn :: (a -> b) -> [a] -> [a], for comparable b
Examples
lib.lists.sortOn usage example
sortOn stringLength [ "aa" "b" "cccc" ]
=> [ "b" "aa" "cccc" ]
Noogle detected
Implementation
The following is the current implementation of this function.
sortOn = f: list:
let
# Heterogenous list as pair may be ugly, but requires minimal allocations.
pairs = map (x: [(f x) x]) list;
in
map
(x: builtins.elemAt x 1)
(sort
# Compare the first element of the pairs
# Do not factor out the `<`, to avoid calls in hot code; duplicate instead.
(a: b: head a < head b)
pairs);