SPARKPOND / GUIDE
How to Remove Duplicate Rows from a CSV
Duplicates must be defined by all columns or by stable business keys before rows are removed.
Problem symptoms
- Repeated emails inflate counts.
- Monthly merges contain the same record twice.
Why it happens
- Repeated exports.
- Form resubmission.
- Several systems share the same identifier.
Example before and after
Before
id,email 1,a@example.com 1,a@example.com
After
id,email 1,a@example.com
Procedure
- Decide between exact and key-based matching.
- Normalize only fields that should ignore case or spaces.
- Review duplicate groups.
- Choose first, last or most complete and export.
Common mistakes
- Using a non-unique field such as first name.
- Removing duplicates without reviewing legitimate repeated events.
Other possible solutions
- Use CSV Profiler first to measure duplicate patterns.
Important limitations
- Fuzzy record linkage is outside exact CSV deduplication.