Function veho::matrix::mapreduce

pub fn mapreduce<R, M, T, J, F>(
    matrix: M, 
    indicator: J, 
    sequence: F
) -> Option<T> where
    M: IntoIterator<Item = R>,
    R: IntoIterator,
    M::IntoIter: Iterator<Item = R>,
    R::IntoIter: Iterator<Item = R::Item>,
    J: FnMut(R::Item) -> T,
    F: FnMut(T, T) -> T,