Add --to output format option to shaping commands (0.8.0)

CHANGELOG.md

@@ -0,0 +1,58 @@
+# Changelog
+
+All notable changes to this project are listed here. Versions follow [Semantic Versioning](https://semver.org/); until 1.0.0, minor versions may change CLI behaviour.
+
+## [0.8.0] - 2026-10-14
+
+### Added
+
+- `-t, --to json|yaml|csv|ndjson` on every shaping command (`select`, `pick`, `omit`, `rename`, `flatten`, `unflatten`, `filter`, `sort`, `unique`, `head`, `tail`, `group-by`, `count`, `stats`, `join`), so results can be written as YAML, CSV, or NDJSON without a second `to-*` step.
+- This changelog.
+
+### Changed
+
+- When `--to` is not given, shaping commands pick the output format from the `--output` file extension (for example `-o out.csv` writes CSV). Before, they always wrote JSON whatever the file name. Unknown extensions and stdout still get JSON.
+- Writing a non-list result as CSV now fails with a message that points to `--to json` or `--to yaml`.
+
+## [0.7.0] - 2026-10-12
+
+### Added
+
+- `join KEY --with RIGHT_FILE [file]` with `--how inner|left` and `--right-from` to join two arrays of objects on a top-level key.
+
+## [0.6.0] - 2026-10-10
+
+### Added
+
+- `stats FIELD` for count / sum / min / max / avg of a numeric field, on a list or on `group-by` output.
+
+## [0.5.0] - 2026-09-30
+
+### Added
+
+- `group-by KEY`, `count [KEY]`, and `unflatten` (with `--sep`).
+
+## [0.4.0] - 2026-09-28
+
+### Added
+
+- `rename OLD NEW ...`, `flatten` (with `--sep`), `head N`, and `tail N`.
+
+## [0.3.0] - 2026-09-24
+
+### Added
+
+- `filter KEY OP VALUE`, `sort KEY` (with `--desc`), and `unique [KEY]`.
+
+## [0.2.0] - 2026-09-21
+
+### Added
+
+- NDJSON / JSON Lines input and output (`to-ndjson`, `.ndjson` / `.jsonl` detection).
+- `select`, `pick`, and `omit`.
+
+## [0.1.0] - 2026-09-11
+
+### Added
+
+- Python implementation of the CLI: `to-json`, `to-yaml`, `to-csv`, `pretty`, and `minify` with format detection for JSON, YAML, and CSV.

README.md

@@ -46,13 +46,45 @@ After install, the `data-transform` console script is on your `PATH`.
 - `[file]` — input path; omit or use `-` for stdin
 - `-o, --output <file>` — write to a file instead of stdout
 - `-f, --from <format>` — force input format: `json` | `yaml` | `csv` | `ndjson`
-- `--minify` — compact JSON output (`to-json`, `select`, `pick`, `omit`, `rename`, `flatten`, `unflatten`, `filter`, `sort`, `unique`, `head`, `tail`, `group-by`, `count`, `stats`, `join`)
+- `-t, --to <format>` — output format for the shaping commands (everything except `to-*`, `pretty`, and `minify`): `json` | `yaml` | `csv` | `ndjson`. Defaults to the `--output` file extension, else JSON. See [Output formats](#output-formats)
+- `--minify` — compact JSON output (`to-json` and the shaping commands); ignored when the output format is not JSON
 - `--desc` — reverse sort order (`sort` only)
 - `--sep <text>` — separator between nested keys (`flatten` and `unflatten`, default `.`)
 - `-w, --with <file>`, `--how inner|left`, `--right-from <format>` — right-hand file, join type, and right file format (`join` only)
 
 Format is taken from `--from`, else the file extension (`.ndjson` / `.jsonl` → ndjson), else simple content heuristics.
 
+### Output formats
+
+Shaping commands (`select`, `pick`, `omit`, `rename`, `flatten`, `unflatten`, `filter`, `sort`, `unique`, `head`, `tail`, `group-by`, `count`, `stats`, `join`) print JSON by default. Use `-t` / `--to` to write YAML, CSV, or NDJSON directly instead of piping into a `to-*` command.
+
+- The format comes from `--to`, else the `--output` file extension (`.json`, `.yaml` / `.yml`, `.csv`, `.ndjson` / `.jsonl`), else JSON. `--to` always wins, and an unknown extension stays JSON.
+- JSON is pretty-printed unless `--minify` is set. `--minify` does nothing for YAML, CSV, or NDJSON (NDJSON is always one compact value per line).
+- CSV needs a list result. A number, object, or `group-by` result is an error (exit code 1) that suggests `--to json` or `--to yaml` instead.
+- YAML output keeps key order and keeps YAML-only values such as dates, which JSON can't represent.
+
+```bash
+# Filter a CSV and write CSV back out
+data-transform filter age ge 30 people.csv -t csv
+# → name,age
+#   Ada,36
+
+# Format picked from the output file name (events.json is an array of objects)
+data-transform flatten events.json -o events-flat.csv
+data-transform pick id name users.json -o users.yaml
+
+# Unknown extension: name the format with --to
+data-transform sort id users.json -t ndjson -o users.out
+
+# Per-team counts as YAML
+data-transform count team people.json -t yaml
+# → core: 1
+#   web: 1
+
+# Join JSON against CSV and emit CSV
+data-transform join id --with teams.csv users.json -t csv -o report.csv
+```
+
 ## Usage examples
 
 ```bash
@@ -331,6 +363,10 @@ NDJSON (also known as JSON Lines / `.jsonl`) is one JSON value per non-empty lin
 
 CSV support is intentionally small and robust (RFC 4180-ish) via the Python standard library `csv` module: quoted fields, escaped quotes (`""`), and newlines inside quotes. Object arrays use a header row; all cell values are strings when parsed from CSV.
 
+## Changelog
+
+See [CHANGELOG.md](./CHANGELOG.md).
+
 ## Development
 
 ```bash

pyproject.toml

@@ -4,7 +4,7 @@ build-backend = "setuptools.build_meta"
 
 [project]
 name = "data-transform-cli"
-version = "0.7.0"
+version = "0.8.0"
 description = "CLI for YAML ↔ JSON ↔ CSV ↔ NDJSON transforms for pipelines and shell use"
 readme = "README.md"
 license = { text = "MIT" }

src/data_transform/__init__.py

@@ -47,4 +47,4 @@
     "join_rows",
 ]
 
-__version__ = "0.7.0"
+__version__ = "0.8.0"