Skip to content

Instantly share code, notes, and snippets.

@Rich-Harris

Rich-Harris/lookup-vs-nested-foreach.js

Created June 29, 2020 17:44
Show Gist options

  • Select an option

    Learn more about clone URLs
  • Save Rich-Harris/211a6bf8c3697239112261966e640dc6 to your computer and use it in GitHub Desktop.

Select an option

Learn more about clone URLs
Save Rich-Harris/211a6bf8c3697239112261966e640dc6 to your computer and use it in GitHub Desktop.
Download ZIP

Revisions

  1. Rich-Harris created this gist Jun 29, 2020.
    60 changes: 60 additions & 0 deletions lookup-vs-nested-foreach.js
    View file
    Original file line number Diff line number Diff line change
    @@ -0,0 +1,60 @@
    // re https://stackoverflow.com/questions/62621666/how-can-i-reliably-merge-objects-from-these-2-arrays-and-loop-the-resulting-arra/62623714?noredirect=1#comment110766294_62623714

    function with_nested_for_each([a, b]) {
    const result = [];

    a.forEach(p => {
    b.forEach(q => {
    if (p.code === q.code) {
    result.push(Object.assign({}, p, q));
    }
    });
    });

    return result;
    }

    function with_lookup(sources) {
    const codes = new Set( // using a set is an easy way to dedupe
    sources.map(source => source.map(d => d.code)).flat()
    );

    const lookups = sources.map(source => {
    const lookup = new Map();
    source.forEach(d => lookup.set(d.code, d));
    return lookup;
    });

    return Array.from(codes, code => {
    return Object.assign({}, ...lookups.map(d => d.get(code) || {}));
    });
    }

    function test(n) {
    const a = [];
    const b = [];

    for (let i = 0; i < n; i += 1) {
    const code = i;

    a.push({
    code,
    foo: Math.random()
    });

    b.push({
    code,
    bar: Math.random()
    });
    }

    console.time('with_nested_for_each');
    const result_1 = with_nested_for_each([a, b]);
    console.timeEnd('with_nested_for_each');

    console.time('with_lookup');
    const result_2 = with_lookup([a, b]);
    console.timeEnd('with_lookup');

    console.log({ result_1, result_2 });
    }