List Difference (A − B)
Find items in list A that don't appear in list B. The classic 'minus' set operation.
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About List Difference (A − B)
List difference produces items that appear in A but not in B. It's how you find what's been added or what's missing when comparing two snapshots of a list.
When to use it
- Finding new email addresses added to a list
- Identifying items present in one inventory but not another
- Spotting tags that exist in one document but not its sibling
- Computing missing IDs between an expected and actual set
How it works
Both lists are split on LF/CRLF. A Set is built from list B's items. The result is each item from A that is NOT in B, in A's original order, deduplicated.
Examples
Only 'apple' is in A but not in B
A: apple, banana, cherry B: banana, cherry, date
apple
Frequently asked questions
- Is the operation symmetric?
- No. A − B differs from B − A. For items in either-but-not-both (symmetric difference), compute (A − B) and (B − A) separately and concatenate.
- What if A has duplicates?
- Each unique item from A appears once in the result if it's missing from B. The output is a set, not a multiset.