Function rank_no_list

src/expr/src/relation/func.rs:509–557

Like `rank`, but doesn't perform the final wrapping in a list, returning an Iterator instead.

(
    datums: I,
    callers_temp_storage: &'b RowArena,
    order_by: &[ColumnOrder],
)

/// Like `rank`, but doesn't perform the final wrapping in a list, returning an Iterator
/// instead.
fn rank_no_list<'a: 'b, 'b, I>(
    datums: I,
    callers_temp_storage: &'b RowArena,
    order_by: &[ColumnOrder],
) -> impl Iterator<Item = Datum<'b>>
where
    I: IntoIterator<Item = Datum<'a>>,
{
    // Keep the row used for ordering around, as it is used to determine the rank
    let datums = order_aggregate_datums_with_rank(datums, order_by);

    let mut datums = datums
        .into_iter()
        .map(|(d0, order_row)| {
            d0.unwrap_list()
                .iter()
                .map(move |d1| (d1, order_row.clone()))
        })
        .flatten();

    callers_temp_storage.reserve(datums.size_hint().0);
    datums
        .next()
        .map_or(vec![], |(first_datum, first_order_row)| {
            // Folding with (last order_by row, last assigned rank,
            // row number, output vec)
            datums.fold(
                (first_order_row, 1, 1, vec![(first_datum, 1)]),
                |mut acc, (next_datum, next_order_row)| {
                let (ref mut acc_row, ref mut acc_rank, ref mut acc_row_num, ref mut output) = acc;
                *acc_row_num += 1;
                // Identity is based on the order_by expression
                if *acc_row != next_order_row {
                    *acc_rank = *acc_row_num;
                    *acc_row = next_order_row;
                }

                (*output).push((next_datum, *acc_rank));
                acc
            })
        }.3).into_iter().map(|(d, i)| {
        callers_temp_storage.make_datum(|packer| {
            packer.push_list_with(|packer| {
                packer.push(Datum::Int64(i));
                packer.push(d);
            });
        })
    })
}

/// The expected input is in the format of `[((OriginalRow, [EncodedArgs]), OrderByExprs...)]`
/// The output is in the format of `[result_value, original_row]`.