What is the difference between Union and Intersection?

Union is everything from either list (unique). Intersection is only values that appear in both lists.

Merge two lists into one unique list

Last updated: 2026-08-26

Combining two exports often leaves repeats: yesterday’s customers plus today’s signups, or two regional SKU files. In ListDiff, that job is the Union tab—one combined set of unique values after you compare.

Steps

Paste source one into List A and source two into List B.
Leave trim and ignore-empty on so padding and blank lines do not create fake “new” rows.
Optionally turn on Dedupe so each side is treated as a set before compare.
Click Compare lists, open Union, then copy or download.

When Union is the wrong tab

Need only the overlap → use Intersection.
Need “in A but not B” (for example suppression cleanup) → use A only.
Need repeats inside one file → see find duplicates.

Example

A: red, blue
B: blue, green
Union: red, blue, green

Paste lists to merge

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FAQ

How do I merge two lists without duplicates?

Compare both sides, then copy the Union result.

Union vs Intersection?

Union = either list. Intersection = both lists. See Compare basics.