87 lines
3.1 KiB
JavaScript
87 lines
3.1 KiB
JavaScript
import { BaseRetriever } from "@langchain/core/retrievers";
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/**
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* Ensemble retriever that aggregates and orders the results of
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* multiple retrievers by using weighted Reciprocal Rank Fusion.
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*/
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export class EnsembleRetriever extends BaseRetriever {
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static lc_name() {
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return "EnsembleRetriever";
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}
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constructor(args) {
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super(args);
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Object.defineProperty(this, "lc_namespace", {
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enumerable: true,
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configurable: true,
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writable: true,
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value: ["langchain", "retrievers", "ensemble_retriever"]
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});
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Object.defineProperty(this, "retrievers", {
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enumerable: true,
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configurable: true,
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writable: true,
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value: void 0
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});
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Object.defineProperty(this, "weights", {
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enumerable: true,
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configurable: true,
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writable: true,
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value: void 0
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});
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Object.defineProperty(this, "c", {
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enumerable: true,
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configurable: true,
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writable: true,
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value: 60
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});
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this.retrievers = args.retrievers;
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this.weights =
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args.weights ||
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new Array(args.retrievers.length).fill(1 / args.retrievers.length);
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this.c = args.c || 60;
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}
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async _getRelevantDocuments(query, runManager) {
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return this._rankFusion(query, runManager);
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}
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async _rankFusion(query, runManager) {
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const retrieverDocs = await Promise.all(this.retrievers.map((retriever, i) => retriever.invoke(query, {
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callbacks: runManager?.getChild(`retriever_${i + 1}`),
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})));
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const fusedDocs = await this._weightedReciprocalRank(retrieverDocs);
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return fusedDocs;
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}
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async _weightedReciprocalRank(docList) {
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if (docList.length !== this.weights.length) {
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throw new Error("Number of retrieved document lists must be equal to the number of weights.");
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}
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const rrfScoreDict = docList.reduce((rffScore, retrieverDoc, idx) => {
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let rank = 1;
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const weight = this.weights[idx];
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while (rank <= retrieverDoc.length) {
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const { pageContent } = retrieverDoc[rank - 1];
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if (!rffScore[pageContent]) {
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// eslint-disable-next-line no-param-reassign
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rffScore[pageContent] = 0;
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}
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// eslint-disable-next-line no-param-reassign
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rffScore[pageContent] += weight / (rank + this.c);
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rank += 1;
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}
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return rffScore;
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}, {});
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const uniqueDocs = this._uniqueUnion(docList.flat());
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const sortedDocs = Array.from(uniqueDocs).sort((a, b) => rrfScoreDict[b.pageContent] - rrfScoreDict[a.pageContent]);
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return sortedDocs;
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}
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_uniqueUnion(documents) {
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const documentSet = new Set();
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const result = [];
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for (const doc of documents) {
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const key = doc.pageContent;
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if (!documentSet.has(key)) {
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documentSet.add(key);
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result.push(doc);
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}
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}
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return result;
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}
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}
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