@jahed/sparql-engine/dist/operators/sparql-distinct.js

SPARQL query engine for servers and web browsers.

// SPDX-License-Identifier: MIT
import { termToString } from "rdf-string";
import { Pipeline } from "../engine/pipeline/pipeline.js";
import { Bindings } from "../rdf/bindings.js";
/**
 * Hash an set of mappings and produce an unique value
 * @private
 * @param item - The item to hash
 * @return An unique hash which identify the item
 */
function _hash(bindings) {
    const items = [];
    bindings.forEach((k, v) => items.push(`${k}=${encodeURIComponent(termToString(v))}`));
    items.sort();
    return items.join("&");
}
/**
 * Applies a DISTINCT modifier on the output of another operator.
 * @see {@link https://www.w3.org/TR/2013/REC-sparql11-query-20130321/#modDuplicates}
 * @param source - Input {@link PipelineStage}
 * @return A {@link PipelineStage} which evaluate the DISTINCT operation
 */
export default function sparqlDistinct(source) {
    return Pipeline.getInstance().distinct(source, (bindings) => _hash(bindings));
}
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