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javascriptarraysset-difference

What is the fastest or most elegant way to compute a set difference using Javascript arrays?

Let A and B be two sets. I'm looking for really fast or elegant ways to compute the set difference (A - B or A \B, depending on your preference) between them. The two sets are stored and manipulated as Javascript arrays, as the title says.

Notes:

  • Gecko-specific tricks are okay
  • I'd prefer sticking to native functions (but I am open to a lightweight library if it's way faster)
  • I've seen, but not tested, JS.Set (see previous point)

Edit: I noticed a comment about sets containing duplicate elements. When I say "set" I'm referring to the mathematical definition, which means (among other things) that they do not contain duplicate elements.

Solution

  • I don't know if this is most effective, but perhaps the shortest:

    var A = [1, 2, 3, 4];
var B = [1, 3, 4, 7];

var diff = A.filter(function(x) {
  return B.indexOf(x) < 0;
});

console.log(diff); // [2]

    Updated to ES6:

    const A = [1, 2, 3, 4];
const B = [1, 3, 4, 7];

const diff = A.filter(x => !B.includes(x));

console.log(diff); // [2]