Function sharpen::classify_::classify

pub fn classify<'a, Input, FnT, TT: 'a, TC, TRes>(
    input: Input, 
    fnx: FnT
) -> TRes where
    Input: IntoIterator<Item = TT>,
    FnT: FnMut(&TT) -> TC,
    TC: Copy + Default + PartialEq,
    TRes: FromIterator<(TC, Vec<TT>)>,