fill

Fills empty or null values with specified values or strategies (forward-fill, backward-fill).

Write with --output. A trailing path is not a positional argument.

# Fill with constant value
undatum fill data.csv --fields name,email --value "N/A" --output output.csv

# Forward fill (use previous value)
undatum fill data.jsonl --fields status --strategy forward --output output.jsonl

# Backward fill (use next value)
undatum fill data.csv --fields category --strategy backward --output output.csv

Reference

Reads: any readable format · Writes: any writable format; CSV/TSV/JSON/JSON Lines on stdout · Memory: streaming; --strategy backward spills to disk · Engines: auto, duckdb, python

undatum fill [OPTIONS] INPUT_FILE

Argument	Description
INPUT_FILE	Path to input file. (required)

Option	Description	Default
-o, --output TEXT	Optional output file path. If not specified, prints to stdout.
-f, --fields TEXT	Comma-separated list of field names to fill (default: all fields).
--strategy TEXT	Fill strategy: 'constant' (default), 'forward', or 'backward'.	constant
--value TEXT	Constant value to use for filling (required for 'constant' strategy).
-d, --delimiter TEXT	CSV delimiter character (auto-detected when omitted).
--quotechar TEXT	CSV quote character (iterabledata default '"' when omitted).
--encoding TEXT	File encoding (e.g., 'utf8', 'latin1').
--verbose / --no-verbose	Enable verbose logging output.	--no-verbose
-F, --format-in TEXT	Override input file format detection (e.g., 'csv', 'jsonl').
--table, --sheet TEXT	Table or sheet name for multi-table sources (Excel, SQLite, lakehouse).
--start-page INTEGER	Sheet index (0-based) for Excel files.	0
--trust	Acknowledge pickle deserialization risk when reading pickle sources.
--on-error TEXT	Parse-error policy: raise (default), skip, or warn.
--error-log TEXT	Append parse errors as JSONL (use with --on-error skip or warn).
--flatten-nested	Unfold nested dict / array-of-dict fields into dotted paths (e.g. city.lat).
--max-nested-depth INTEGER	With --flatten-nested, maximum nest depth to unfold (engine default 5).
--keep-nested-parents / --no-keep-nested-parents	With --flatten-nested, keep parent dict/array fields alongside dotted children.	--keep-nested-parents
-e, --engine [auto|duckdb|python]	Processing engine: auto (default), duckdb, or python.
-O, --format-out TEXT	Output format (e.g. csv, jsonl, parquet). Defaults to the --output extension, or to the input's text format on stdout.

See also shared options.