Function dataflow::render::reduce::build_basic_aggregate

fn build_basic_aggregate<G>(
    input: Collection<G, (Row, Row)>, 
    index: usize, 
    aggr: &AggregateExpr
) -> Arranged<G, TraceAgent<OrdValSpine<Row, Row, <G as ScopeParent>::Timestamp, Diff, usize>>> where
    G: Scope,
    G::Timestamp: Lattice, 

Build the dataflow to compute a single basic aggregation.

This method also applies distinctness if required.