Array intersection based on function

OSCC · JavaScript, Array · Oct 20, 2020

Returns the elements that exist in both arrays, after applying the provided function to each array element of both.

  • Create a Set by applying fn to all elements in b.
  • Use Array.prototype.filter() on a to only keep elements, which produce values contained in b when fn is applied to them.
const intersectionBy = (a, b, fn) => {
  const s = new Set(b.map(fn));
  return [...new Set(a)].filter(x => s.has(fn(x)));
};
intersectionBy([2.1, 1.2], [2.3, 3.4], Math.floor); // [2.1]
intersectionBy(
  [{ title: 'Apple' }, { title: 'Orange' }],
  [{ title: 'Orange' }, { title: 'Melon' }],
  x => x.title
); // [{ title: 'Orange' }]

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