Getting a union of two arrays in JavaScript

With the arrival of ES6 with sets and splat operator (at the time of being works only in Firefox, check compatibility table), you can write the following cryptic one liner:

var a = [34, 35, 45, 48, 49];
var b = [48, 55];
var union = [...new Set([...a, ...b])];
console.log(union);

Little explanation about this line: [...a, ...b] concatenates two arrays, you can use a.concat(b) as well. new Set() create a set out of it and thus your union. And the last [...x] converts it back to an array.


If you don't need to keep the order, and consider 45 and "45" to be the same:

function union_arrays (x, y) {
  var obj = {};
  for (var i = x.length-1; i >= 0; -- i)
     obj[x[i]] = x[i];
  for (var i = y.length-1; i >= 0; -- i)
     obj[y[i]] = y[i];
  var res = []
  for (var k in obj) {
    if (obj.hasOwnProperty(k))  // <-- optional
      res.push(obj[k]);
  }
  return res;
}

console.log(union_arrays([34,35,45,48,49], [44,55]));

Tags:

Javascript

Arrays

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