Add CSV lookup values and keep unmatched rows
Enrich CSV records from a unique reference key, retain unmatched records, and make missing lookup values visible in Python.
Example files includedFind the fix for your file.
Common spreadsheet problems, explained one step at a time.
All guides
Guides 1–12 of 61
Append CSV files with matching headers safely
Append exports only when their column names and order match, keep one header, and stop if a source file changes its schema.
Example files included
Combine CSV files when columns are in a different order
Append CSV exports by header name with a small Python script that rejects duplicate headers, schema changes, and incomplete rows.
Example files included
Compare CSV snapshots by ID
Compare two keyed CSV snapshots in Python and separate new IDs, missing IDs, and changed field values without relying on row order.
Example files included
Convert CSV percentage strings to decimal fractions
Parse explicitly marked percentage values in Python, divide once by 100, and avoid confusing 12.5 percent with the fraction 12.5.
Example files included
Convert CSV to JSON records without guessing types
Convert a CSV table into a JSON array in Python while preserving identifiers, checking headers, and leaving numeric conversion explicit.
Example files included
Convert day/month dates without guessing ambiguous rows
Resolve ambiguous imported dates with an explicit day/month rule, a validation formula, and a downloadable example with invalid-date cases.
Example files included
Convert flat JSON records to CSV with fixed columns
Choose a column order for flat JSON objects, reject unexpected fields, and write CSV with deliberate handling of null and nested values.
Example files included
Convert TSV to CSV without breaking commas in values
Use a tab-aware reader and a comma-aware writer to convert TSV into CSV while preserving punctuation inside the original fields.
Example files included
Convert Unix timestamps: seconds or milliseconds?
Convert integer Unix timestamps to UTC in Python, require the documented unit, and preserve millisecond precision without float division.
Example files included
Count CSV records by category and reconcile the total
Build a frequency table from CSV categories in Python, keep blank categories visible, and check that the counts cover every source record.
Example files included
CSV opens in one column? Identify the delimiter first
Compare comma, semicolon, and tab examples, preserve quoted fields, and select the right import separator without editing the original data.
Example files included