Function dataflow::render::reduce::build_distinct_retractions

fn build_distinct_retractions<G, T>(
    collection: Collection<G, (Row, Row)>
) -> Collection<G, Row> where
    G: Scope,
    G::Timestamp: Lattice + Refines<T>,
    T: Timestamp + Lattice, 

Build the dataflow to compute the set of distinct keys.

This implementation maintains the rows that don’t appear in the output.