Function polars_utils::sort::perfect_sort

pub unsafe fn perfect_sort(
    pool: &ThreadPool, 
    idx: &[(IdxSize, IdxSize)]
) -> Vec<IdxSize>

This is a perfect sort particularly useful for an argsort of an argsort The second argsort sorts indices from 0 to len so can be just assigned to the new index location.

Besides that we know that all indices are unique ang thus not alias so we can parallelize.

This sort does not sort in place and will allocate.

• The right indices are used for sorting
• The left indices are placed at the location right points to.

Safety

The caller must ensure that the right indexes fo &[(_, IdxSize)] are integers ranging from 0..idx.len