Function into_group_map_by_with_hasher 

pub fn into_group_map_by_with_hasher<I, K, V, F, S>(
    iter: I,
    f: F,
    hash_builder: S,
) -> HashMap<K, Vec<V>, S>
where
    I: Iterator<Item = V>,
    K: Hash + Eq,
    F: FnMut(&V) -> K,
    S: BuildHasher,