n3wt0n!

Say you’ve got a column of data

Hello
Hi
Heya
Yo
Hi
Hey

and you want to find duplicate entries within the column

Hello	FALSE
Hi	TRUE
Heya	FALSE
Yo	FALSE
Hi	TRUE
Hey	FALSE

Google Docs flagged Hi as being a duplicate. How? COUNTIF.

For this example the data starts in A1 and Column B is empty. So type

=COUNTIF(A:A,A1)>1

into B1. You should now see FALSE in that cell. Now copy B1 beside all the other cells you want to test for duplicates.