CSV Columns to List Converter

Extracting a single column from a CSV file and reformatting it as a flat list is a frequent task in data migration, SQL query building, and API payload construction. Manual copy-paste from spreadsheets introduces invisible characters, broken encodings, and missed rows. This tool parses CSV input according to RFC 4180 rules, correctly handling quoted fields that contain embedded commas or newlines. It auto-detects the delimiter (comma, semicolon, tab, or pipe) by frequency analysis across the first 5 rows, then presents every detected column for selection.

The output list supports configurable item separators (sep), optional quoting wrappers, prefix and suffix strings, and deduplication. Note: the parser assumes UTF-8 encoding. Files with BOM markers are stripped automatically. For files exceeding 10 MB, consider splitting before upload. Pro Tip: when building SQL IN clauses, set the wrapper to single quotes and separator to comma to get a ready-to-paste value list.

The delimiter auto-detection algorithm scores each candidate delimiter by counting occurrences per line and measuring consistency:

where d = candidate delimiter, n_d = mean count of d per line across the sample rows, and σ_d = standard deviation of counts per line. A low σ (consistent count across rows) and high n (frequent occurrence) yields the highest score. The delimiter with the maximum score is selected.

The RFC 4180 field parser follows this state machine: if a field begins with a double-quote character ("), all characters until the next unescaped " are captured, where "" is treated as a literal embedded quote. Fields not beginning with " terminate at the next delimiter or line break. The deduplication pass, when enabled, uses a Set structure with O(1) average lookup per item, yielding total complexity O(n) for n rows.