@electric-sql/d2mini/dist/operators/filter.js

D2Mini is a minimal implementation of Differential Dataflow for performing in-memory incremental view maintenance.

import { DifferenceStreamWriter } from '../graph.js';
import { StreamBuilder } from '../d2.js';
import { LinearUnaryOperator } from '../graph.js';
/**
 * Operator that filters elements from the input stream
 */
export class FilterOperator extends LinearUnaryOperator {
    #f;
    constructor(id, inputA, output, f) {
        super(id, inputA, output);
        this.#f = f;
    }
    inner(collection) {
        return collection.filter(this.#f);
    }
}
/**
 * Filters elements from the input stream
 * @param f - The predicate to filter elements
 */
export function filter(f) {
    return (stream) => {
        const output = new StreamBuilder(stream.graph, new DifferenceStreamWriter());
        const operator = new FilterOperator(stream.graph.getNextOperatorId(), stream.connectReader(), output.writer, f);
        stream.graph.addOperator(operator);
        stream.graph.addStream(output.connectReader());
        return output;
    };
}
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