@electric-sql/d2mini/dist/operators/count.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 { ReduceOperator } from './reduce.js';
/**
 * Operator that counts elements by key (version-free)
 */
export class CountOperator extends ReduceOperator {
    constructor(id, inputA, output) {
        const countInner = (vals) => {
            let count = 0;
            for (const [_, diff] of vals) {
                count += diff;
            }
            return [[count, 1]];
        };
        super(id, inputA, output, countInner);
    }
}
/**
 * Counts the number of elements by key (version-free)
 */
export function count() {
    return (stream) => {
        const output = new StreamBuilder(stream.graph, new DifferenceStreamWriter());
        const operator = new CountOperator(stream.graph.getNextOperatorId(), stream.connectReader(), output.writer);
        stream.graph.addOperator(operator);
        stream.graph.addStream(output.connectReader());
        return output;
    };
}
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