Fixed dropping the geometry column (#322)

CHANGELOG.md

@@ -9,6 +9,11 @@ Packaging:
 - `dask>=2025.1.0` is now required.
 - `python>=3.10` is now required.
 
+Bug fixes:
+
+- Fixed `GeoDataFrame.drop` returning a `GeoDataFrame`
+  instead of a `DataFrame`, when dropping the geometry
+  column (#321).
 
 Version 0.4.2 (September 24, 2024)
 ----------------------------------

dask_geopandas/_expr.py

@@ -0,0 +1,24 @@
+from typing import Literal
+
+import dask.dataframe.dask_expr as dx
+
+import geopandas
+
+
+def _drop(df: geopandas.GeoDataFrame, columns, errors):
+    return df.drop(columns=columns, errors=errors)
+
+
+def _validate_axis(axis=0, none_is_zero: bool = True) -> None | Literal[0, 1]:
+    if axis not in (0, 1, "index", "columns", None):
+        raise ValueError(f"No axis named {axis}")
+    # convert to numeric axis
+    numeric_axis: dict[str | None, Literal[0, 1]] = {"index": 0, "columns": 1}
+    if none_is_zero:
+        numeric_axis[None] = 0
+
+    return numeric_axis.get(axis, axis)
+
+
+class Drop(dx.expr.Drop):
+    operation = staticmethod(_drop)

dask_geopandas/expr.py

@@ -26,6 +26,7 @@
 
 import dask_geopandas
 
+from ._expr import Drop, _validate_axis
 from .geohash import _geohash
 from .hilbert_distance import _hilbert_distance
 from .morton_distance import _morton_distance
@@ -868,6 +869,25 @@ def explode(self, column=None, ignore_index=False, index_parts=None):
             enforce_metadata=False,
         )
 
+    @derived_from(geopandas.GeoDataFrame)
+    def drop(self, labels=None, axis=0, columns=None, errors="raise"):
+        # https://github.com/geopandas/dask-geopandas/issues/321
+        # Override to avoid an inplace drop, since we need
+        # to convert from a GeoDataFrame to a DataFrame when dropping
+        # the geometry column.
+        if columns is None and labels is None:
+            raise TypeError("must either specify 'columns' or 'labels'")
+
+        axis = _validate_axis(axis)
+
+        if axis == 1:
+            columns = labels or columns
+        elif axis == 0 and columns is None:
+            raise NotImplementedError(
+                "Drop currently only works for axis=1 or when columns is not None"
+            )
+        return new_collection(Drop(self, columns=columns, errors=errors))
+
 
 from_geopandas = dd.from_pandas
 

dask_geopandas/tests/test_core.py

@@ -1034,6 +1034,21 @@ def get_chunk(n):
     assert_geodataframe_equal(ddf.compute(), expected)
 
 
+def test_drop():
+    # https://github.com/geopandas/dask-geopandas/issues/321
+    df = dask_geopandas.from_geopandas(
+        geopandas.GeoDataFrame({"col": [1], "geometry": [Point(1, 1)]}), npartitions=1
+    )
+    result = df.drop(columns="geometry")
+    assert type(result) is dd.DataFrame
+
+    result = df.drop(columns="col")
+    assert type(result) is dask_geopandas.GeoDataFrame
+
+    with pytest.raises(ValueError, match="No axis named x"):
+        df.drop(labels="a", axis="x")
+
+
 def test_core_deprecated():
     with pytest.warns(FutureWarning, match="dask_geopandas.core"):
         import dask_geopandas.core  # noqa: F401

pyproject.toml

@@ -155,6 +155,6 @@ section-order = [
 ]
 
 [tool.ruff.lint.isort.sections]
-"dask" = ["dask", "dask_expr"]
+"dask" = ["dask"]
 "geo" = ["geopandas", "shapely", "pyproj"]
 "testing" = ["pytest", "pandas.testing", "numpy.testing", "geopandas.tests", "geopandas.testing"]