Sometimes you want to find duplicate rows in a Google spreadsheet, but don’t want to examine every column — maybe you want to exclude a timestamp or other columns.
This Google Apps Script takes a list of columns that you care about. Then it temporarily copies those columns to a new sheet, looks for duplicates, highlights the duplicate rows in red on the main sheet, and removes the temporary sheet.
The script is attached to this Google Spreadsheet. Make a copy of this sheet, or just copy the script. You can do that by going to Tools – Script Editor and copying the script to the script editor of your own spreadsheet. Then edit the line that defines the important columns. After you re-open your spreadsheet, the “My Scripts” menu will show up. The first time you run the script, it will bring up the permissions dialog. You’ll need to run it again to make it work.
Here’s a video of it in action: