Explicit support for curvefit (#337)

cf_xarray/accessor.py

@@ -15,6 +15,7 @@
     List,
     Mapping,
     MutableMapping,
+    Sequence,
     TypeVar,
     Union,
     cast,
@@ -1059,6 +1060,52 @@ def _get_all_cell_measures(self):
 
         return self._all_cell_measures
 
+    def curvefit(
+        self,
+        coords: str | DataArray | Iterable[str | DataArray],
+        func: Callable[..., Any],
+        reduce_dims: Hashable | Iterable[Hashable] = None,
+        skipna: bool = True,
+        p0: dict[str, Any] = None,
+        bounds: dict[str, Any] = None,
+        param_names: Sequence[str] = None,
+        kwargs: dict[str, Any] = None,
+    ):
+
+        if coords is not None:
+            if isinstance(coords, str):
+                coords = (coords,)
+            coords = [
+                apply_mapper(  # type: ignore
+                    [_single(_get_coords)], self._obj, v, error=False, default=[v]  # type: ignore
+                )[
+                    0
+                ]  # type: ignore
+                for v in coords
+            ]
+        if reduce_dims is not None:
+            if isinstance(reduce_dims, Hashable):
+                reduce_dims: Iterable[Hashable] = (reduce_dims,)  # type: ignore
+            reduce_dims = [
+                apply_mapper(  # type: ignore
+                    [_single(_get_dims)], self._obj, v, error=False, default=[v]  # type: ignore
+                )[
+                    0
+                ]  # type: ignore
+                for v in reduce_dims  # type: ignore
+            ]
+
+        return self._obj.curvefit(
+            coords=coords,
+            func=func,
+            reduce_dims=reduce_dims,
+            skipna=skipna,
+            p0=p0,
+            bounds=bounds,
+            param_names=param_names,
+            kwargs=kwargs,
+        )
+
     def _process_signature(
         self,
         func: Callable,

cf_xarray/tests/__init__.py

@@ -63,6 +63,7 @@ def LooseVersion(vstring):
     return version.LooseVersion(vstring)
 
 
-has_pint, requires_pint = _importorskip("pint")
-has_shapely, requires_shapely = _importorskip("shapely")
 has_cftime, requires_cftime = _importorskip("cftime")
+has_scipy, requires_scipy = _importorskip("scipy")
+has_shapely, requires_shapely = _importorskip("shapely")
+has_pint, requires_pint = _importorskip("pint")

cf_xarray/tests/test_accessor.py

@@ -30,7 +30,7 @@
     romsds,
     vert,
 )
-from . import raise_if_dask_computes, requires_cftime, requires_pint
+from . import raise_if_dask_computes, requires_cftime, requires_pint, requires_scipy
 
 mpl.use("Agg")
 
@@ -1619,3 +1619,26 @@ def test_cf_role():
 
     dsg.foo.cf.plot(x="profile_id")
     dsg.foo.cf.plot(x="trajectory_id")
+
+
+@requires_scipy
+def test_curvefit():
+    from cf_xarray.datasets import airds
+
+    def line(time, slope):
+        t = (time - time[0]).astype(float)
+        return slope * t
+
+    actual = airds.air.cf.isel(lat=4, lon=5).curvefit(coords=("time",), func=line)
+    expected = airds.air.cf.isel(lat=4, lon=5).cf.curvefit(coords="T", func=line)
+    assert_identical(expected, actual)
+
+    def plane(coords, slopex, slopey):
+        x, y = coords
+        return slopex * (x - x.mean()) + slopey * (y - y.mean())
+
+    actual = airds.air.isel(time=0).curvefit(coords=("lat", "lon"), func=plane)
+    expected = airds.air.isel(time=0).cf.curvefit(
+        coords=("latitude", "longitude"), func=plane
+    )
+    assert_identical(expected, actual)

ci/environment.yml

@@ -11,5 +11,6 @@ dependencies:
   - pandas
   - pint
   - pooch
+  - scipy
   - shapely
   - xarray

setup.cfg

@@ -45,6 +45,8 @@ known_first_party = cf_xarray
 known_third_party = dask,matplotlib,numpy,pandas,pint,pytest,setuptools,sphinx_autosummary_accessors,xarray
 
 # Most of the numerical computing stack doesn't have type annotations yet.
+[mypy]
+allow_redefinition = True
 [mypy-affine.*]
 ignore_missing_imports = True
 [mypy-bottleneck.*]