import type { VariableTerm } from "sparqljs";
import type { PipelineStage } from "../engine/pipeline/pipeline-engine.ts";
import { Bindings } from "../rdf/bindings.ts";
import type { EngineTripleValue } from "../types.ts";
export type Group = Record<string, EngineTripleValue[]>;
/**
 * Apply a SPARQL GROUP BY clause
 * @see {@link https://www.w3.org/TR/sparql11-query/#groupby}
 * @param source - Input {@link PipelineStage}
 * @param variables - GROUP BY variables
 * @return A {@link PipelineStage} which evaluate the GROUP BY operation
 */
export default function sparqlGroupBy(source: PipelineStage<Bindings>, variables: VariableTerm[]): PipelineStage<Bindings>;