Function flatnonzero 

pub fn flatnonzero<T, D>(a: &Array<T, D>) -> Vec<usize>
where
    T: Element + PartialEq,
    D: Dimension,

Return the indices of non-zero elements in the flattened array.

Equivalent to np.flatnonzero(a). An element is “non-zero” if it is not equal to the type’s zero value.