Compare two lists

Three answers, not one

"Compare two lists" almost always means one of three different questions, and which one matters changes with the task:

• In both — the overlap. Who is on the invite list and also already a customer.
• Only in list A — what the first list has that the second is missing. Invoices we sent that the bank statement does not show.
• Only in list B — the reverse. Charges on the statement with no invoice behind them.

All three are computed at once, each with its own count and its own copy and download buttons, because the useful next step is usually to paste one of them somewhere else.

Case, whitespace and duplicates

Leading and trailing spaces are always trimmed — a value copied out of a spreadsheet usually carries one, and "matching" that fails on an invisible space wastes an afternoon. Upper and lower case are treated as different unless you turn that off, which matters for email lists, where Bob@example.com and bob@example.com are the same mailbox.

Repeats inside one list are collapsed, and the count of what was collapsed is shown — a list of 500 emails that turns out to hold 40 duplicates is itself a finding.

Doing the same thing in Excel, and why people stop

The classic spreadsheet approach is =COUNTIF(B:B, A2)>0 in a helper column, or a VLOOKUP wrapped in IFERROR. It works, and it comes with the usual costs: a helper column you have to remember to delete, absolute references that break when someone sorts the sheet, and a result that answers only one of the three questions above at a time. Running it in the other direction means writing it again on the other sheet.

For a one-off check, paste and read. For work you repeat, a formula column that recalculates is the right shape — that is what the Match panel in TableDI writes for you, in four steps, without you having to remember the argument order. How the formula panel works.

Nothing leaves this tab

Lists pasted into comparison sites are usually email addresses, customer IDs or account numbers. This page computes the answer in your browser as you type — there is no request to send, so nothing to intercept, log or retain.