frankiehayward
12/5/2019 - 10:15 PM

differenceBy

This method returns the difference between two arrays, after applying a given function to each element of both lists.

difference_by.js
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const differenceBy = (a, b, fn) => {
  const s = new Set(b.map(fn));
  return a.filter(x => !s.has(fn(x)));
};

differenceBy([2.1, 1.2], [2.3, 3.4], Math.floor); // [1.2]
differenceBy([{ x: 2 }, { x: 1 }], [{ x: 1 }], v => v.x); // [ { x: 2 } ]