max_by

In std/seq.

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

The value of self that is greatest, 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"] | max_by(s => size(s)) is "ccc".