Get the Difference between Two Sets using JavaScript

Get the Difference between Two Sets #

To get the difference between two Sets:

1. Convert the first Set to an Array.
2. Use the filter() method to iterate over the array.
3. Use the has() method to check if each element is not contained in the second Set.
4. Convert the array back to a Set.

Copied!
function getDifference(setA, setB) {
  return new Set(
    [...setA].filter(element => !setB.has(element))
  );
}

const set1 = new Set(['a', 'b', 'c']);
const set2 = new Set(['a', 'b']);

console.log(getDifference(set1, set2)); // 👉️ {'c'}

We used the spread syntax (...) to convert the first Set to an array, so we can call the Array.filter method on it.

The function we passed to the filter method gets called with each element in the array.

On each iteration, we check if the element is not contained in the second Set by negating the result from the Set.has() method.

The has() method returns true if the element is contained in the Set, and false otherwise.

Copied!
function getDifference(setA, setB) {
  return new Set(
    [...setA].filter(element => !setB.has(element))
  );
}

const set1 = new Set(['a']);
const set2 = new Set(['a', 'b', 'c']);

console.log(getDifference(set1, set2)); // 👉️ {}

In the example above, we got an empty Set for the difference, where a Set containing {'b', 'c'} would have been expected.

We only iterated over the first Set, which has 1 element, so we didn't get the complete difference.

Copied!
function getDifference(setA, setB) {
  return new Set(
    [...setA].filter(element => !setB.has(element))
  );
}

const set1 = new Set(['a']);
const set2 = new Set(['a', 'b', 'c']);

const difference = new Set([
  ...getDifference(set1, set2),
  ...getDifference(set2, set1),
]);

console.log(difference); // 👉️ {'b', 'c'}

Here's what we did to get this working:

1. Iterate over the elements of the first Set and return only the elements that are not contained in the second Set.
2. Iterate over the elements of the second Set and return only the elements that are not contained in the first.
3. Combine the results into a third Set.

Now, our example contains the complete difference between the two Set objects.

Further Reading #

• How to add a Key/Value pair to a Map in JavaScript
• Get the Intersection of two Sets using JavaScript