GroupBy.representativeRows

size_t[] representativeRows() @safe pure nothrow

The first-appearance representative row of every distinct key tuple, in discovery order - the frame-level unique keep-first semantics (ADR-2026-10-23-08). Key equality is the grouping's total multi-column equality (nulls equal, NaN equal, signed zero equal).

Returns

the retained global row indices, ascending (row order).