Outer Full Join outside the API, with some performance improvement for some reasons(?)

[patarapolw]

I'm submitting a...

[x] Feature request

Current behavior

According to techfort/LokiJS#688, I tried to implement Full Outer Join in TypeScript, with success; and noticed performance improvement for no reasons. (I have 100K rows, and 4 tables' join is usually around 2-3 sec. It becomes like 1 sec.)

The code is

interface IJoinCollection<T> {
    data: T[];
    key: keyof T;
}

function fullJoin<T, U>(
    colL: IJoinCollection<T>,
    colR: IJoinCollection<U>,
    mapFn: (l: T, r: U) => any,
    isFull: boolean = true
): any[] {
    const joinMapL: any = {};
    const joinMapR: any = {};
    const result: any[] = [];

    for (const rowR of colR.data) {
        const v = rowR[colR.key];

        if (v) {
            joinMapR[v] = joinMapR[v] || [];
            joinMapR[v].push(rowR);
        } else {
            result.push({} as T, rowR);
        }
    }

    for (const rowL of colL.data) {
        const v = rowL[colL.key];

        if (v) {
            for (const vR of joinMapR[v] || [{}]) {
                result.push(mapFn(rowL, vR));
            }

            if (isFull) {
                joinMapL[v] = joinMapL[v] || [];
                joinMapL[v].push(rowL);
            }
        } else {
            result.push(mapFn(rowL, {} as U));
        }
    }

    if (isFull) {
        for (const rowR of colR.data) {
            const v = rowR[colR.key];

            if (v) {
                for (const vL of joinMapL[v] || [{}]) {
                    result.push(mapFn(vL, rowR));
                }
            }
        }
    }

    return result;
}

Environment

LokiDB version: 2.0.0-beta.8 with @lokidb/fs-storage 2.0.0-beta.8
Browser/Node version: Node v11.11.0 Yarn 1.15.2 MacOS