jiayuasu opened a new pull request, #1050:
URL: https://github.com/apache/sedona-db/pull/1050
Adds `DataFrame.unnest(*columns)`, which expands list/array column(s) so
each element becomes its own row — the relational form of pandas/GeoPandas
`explode()`.
```python
df.unnest("vals") # [10, 20, 30] -> 3 rows, other columns repeated
df.unnest("a", "b") # multiple columns unnested in parallel
(position-by-position)
df.unnest("parts") # ST_Dump(geom) -> one row per part (spatial explode)
```
## Design
- Thin wrapper over DataFusion's `DataFrame::unnest_columns`; mirrors the
existing `drop_columns` binding.
- **Engine-neutral naming** (`unnest`, matching Ibis / DuckDB SQL `UNNEST`)
rather than the pandas-flavored `explode`, consistent with the relational
DataFrame surface.
- Clear errors: no arguments -> `ValueError`; non-str argument ->
`TypeError`; unknown column -> `SedonaError` ("No field named …"); a raw
geometry (Binary) column -> `SedonaError` (unnest a multi-geometry via
`ST_Dump` first).
## Tests
New `tests/expr/test_dataframe_unnest.py` (8 tests): list-to-rows expansion,
parallel multi-column unnest, the `ST_Dump` + `unnest` multi-geometry explode,
laziness, and the four error paths. Plus a doctest on the method.
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