Function iter_set::classify_by_key

Important traits for ClassifyByKey<L, R, F>

impl<T, L, R, K, F> Iterator for ClassifyByKey<L, R, F> where
    L: Iterator<Item = T>,
    R: Iterator<Item = T>,
    K: Ord,
    F: FnMut(&T) -> K,  type Item = (Ordering, T);

pub fn classify_by_key<T, L, R, K, F>(
    a: L, 
    b: R, 
    key: F
) -> ClassifyByKey<L::IntoIter, R::IntoIter, F> where
    L: IntoIterator<Item = T>,
    R: IntoIterator<Item = T>,
    K: Ord,
    F: FnMut(&T) -> K, 

Interleave two sorted, deduplicated iterators in sorted order and classify each element according to its source, using a key extraction function.

See classify.