Function merge_sparse_indices 

pub fn merge_sparse_indices<I: Ord, T: Eq, U>(
    left: impl Iterator<Item = (I, T)>,
    right: impl Iterator<Item = (I, T)>,
    operation: impl Fn(T, T) -> U,
    operation_left: impl Fn(T) -> U,
    operation_right: impl Fn(T) -> U,
    is_not_default: impl Fn(&U) -> bool,
) -> Vec<(I, U)>

Collect two sparse iterators by merging them.

Arguments

• left: The first iterator, sorted by index.
• right: The second iterator, sorted by index.
• operation: A binary operation applied when an element is found at some index in both iterators.
• operation_left: A unitary operation applied when an element is found only in the left iterator.
• operation_right: A unitary operation applied when an element is found only in the right iterator.
• is_not_default: A function specifying whether the result if the binary operation is the default value (that is often zero).

Return value

A vector with sparse elements by sorted and unique index.