Function itertools::merge_join_by

pub fn merge_join_by<I, J, F>(
    left: I, 
    right: J, 
    cmp_fn: F
) -> MergeJoinBy<I::IntoIter, J::IntoIter, F> where
    I: IntoIterator,
    J: IntoIterator,
    F: FnMut(&I::Item, &J::Item) -> Ordering, 

Return an iterator adaptor that merge-joins items from the two base iterators in ascending order.

See .merge_join_by() for more information.