flatten

Flattens nested data structures into key-value / dotted-path records (distinct from --flatten-nested on other commands, which unfolds nested fields in place).

undatum flatten data.jsonl
undatum flatten data.jsonl --filter '`type` == "city"' --output flat.jsonl

flatten does not take --flatten-nested (it already emits dotted paths). It does accept --output, --filter, --table / --sheet, --format-in, --quotechar, --trust, --on-error, --error-log, --delimiter, and --encoding. See shared CLI options.