Compare Two Lists

Comparing two lists comes up all the time and is very tedious by eye. Which of last month’s subscribers are missing from this month’s? Which products in the new catalogue were not in the old one? Which names on the guest list have not paid? Which of two sets of tags overlap? Spreadsheets can do it with lookup formulas, but if all you have is two columns of text, pasting them here is quicker.

Putting the lists in

There is one box, with a line of three dashes (—) between the lists:

apple
banana
cherry
---
banana
date

List A goes above the line and list B below. One item per line.

The four results

Only in list A are items that appear in A and not in B. If A is last month’s list and B is this month’s, these are the ones who left.

Only in list B are the opposite: the newcomers.

In both lists is the overlap, which is the answer to “what do these have in common?”

All items combined, no repeats is the union: every item from either list, each once. It is a quick way to merge two lists without duplicates.

Each result shows a count in its heading. If the “in both” result is empty, the lists do not overlap at all, and you may have a formatting problem rather than a real difference, such as one list with trailing spaces or a different case.

Matching rules

Matching is exact unless you change it. By default, upper and lower case are ignored, and spaces at the start and end of each item are trimmed, so “Banana “ and “banana” match. Blank lines are skipped. Items that repeat within a list are counted once. When duplicates differ only by case, the first spelling seen is the one kept in the output.

Order does not matter: the tool compares sets, not sequences. Tick “Sort the results” if you want each result in alphabetical order. If order does matter and you want to see changes in sequence, use the text diff checker instead.

Tips for cleaner results

Lists copied from different sources are usually messy in small ways. Before comparing, run each through remove extra spaces, or use remove duplicate lines and sort lines to tidy it. If one list has extra detail on each line, such as “Smith, John, 2019”, cut it down to the part that identifies the row; the text splitter can divide lines at the commas, and filter lines can remove anything you do not need. Our guide to removing duplicate lines from a list walks through a typical clean-up.