Function duplicates_by_with_hasher 

pub fn duplicates_by_with_hasher<I, Key, F, S>(
    iter: I,
    f: F,
    hash_builder: S,
) -> DuplicatesBy<I, Key, F, S>
where
    Key: Eq + Hash,
    F: FnMut(&I::Item) -> Key,
    I: Iterator,
    S: BuildHasher,

Create a new DuplicatesBy iterator with a specified hash builder.