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difference ​

Problem ​

You have two arrays and need to find items present in the first but not the second — a set-difference operation.

Solution ​

Use difference(source, other, selector?) to return items from source not found in other.

ts
import { difference } from '@vielzeug/arsenal';

difference([1, 2, 3, 4], [2, 4]);
// [1, 3]

const active = [{ id: 1 }, { id: 2 }, { id: 3 }];
const removed = [{ id: 2 }];
difference(active, removed, (u) => u.id);
// [{ id: 1 }, { id: 3 }]

Pitfalls ​

  • Without a selector, uses deep equality for comparison — prefer a selector for large object arrays.
  • Does not deduplicate the result; if source has duplicates, they appear in the output.