min_by

In std/seq.

fn min_by<K : Orderable>(self: Collection<T>, by: T -> K) : Option<T>
fn min_by(self: Collection<T>, by: (T, T) -> Ordering) : Option<T>

The value of self that is least, by the key by gives or by the Ordering by gives two values; the first of equals, or none over an empty collection: ["bb", "a", "ccc"] | min_by(s => size(s)) is "a".