Function mz_expr::permutation_for_arrangement

pub fn permutation_for_arrangement(
    key: &[MirScalarExpr],
    unthinned_arity: usize
) -> (BTreeMap<usize, usize>, Vec<usize>)

Return the map associating columns in the logical, unthinned representation of a collection to columns in the thinned representation of the arrangement corresponding to key.

Returns the permutation and the thinning expression that should be used to create the arrangement.

The permutations and thinning expressions generated here will be tracked in dataflow::plan::AvailableCollections; see the documentation there for more details.