I typically use or recommend the following method:
- Make sure there is a Row ID column.
- Create a single Relation or Query to link similar rows to themselves based on similar values.
- Create a Lookup or Single Value column to retrieve the first matching Row ID from the Relation/Query.
- Finally create an IF column comparing the row’s Row ID to the Lookup/Single Value column and return true if there is a match. Only the first occurrence will be a match.