From structured dataset

docs/api.rst

@@ -55,6 +55,7 @@ UgridDataset
     UgridDataset
     UgridDataset.ugrid
     UgridDataset.from_geodataframe
+    UgridDataset.from_structured
 
 UGRID Accessor
 --------------
@@ -348,7 +349,6 @@ UGRID2D Topology
     Ugrid2d.to_dataset
     Ugrid2d.from_geodataframe
     Ugrid2d.from_structured
-    Ugrid2d.from_structured_multicoord
     Ugrid2d.from_structured_bounds
     Ugrid2d.from_structured_intervals1d
     Ugrid2d.from_structured_intervals2d

docs/changelog.rst

@@ -6,6 +6,26 @@ All notable changes to this project will be documented in this file.
 The format is based on `Keep a Changelog`_, and this project adheres to
 `Semantic Versioning`_.
 
+Unreleased
+----------
+
+Changed
+~~~~~~~
+
+- :meth:`xugrid.UgridDataArrayAccessor.from_structured` previously required the
+  literal dimensions ``("y", "x")``. This requirement has been relaxed, it will
+  now infer the dimensions from the provided coordinates.
+- :meth:`xugrid.Ugrid2d.from_structured` previously only supported 1D
+  coordinates; it now detects whether coordinates are 1D or 2D automatically.
+  Accordingly, :meth:`xugrid.Ugrid2d.from_structured_multicoord` should no
+  longer be used, and calling it will give a FutureWarning.
+
+Added
+~~~~~
+
+- :meth:`xugrid.UgridDataset.from_structured` has been added to create
+  UgriDatasets from xarray Datasets.
+
 [0.12.1] 2024-09-09
 -------------------
 
@@ -78,7 +98,7 @@ Changed
 - Selection operations such as :meth:`UgridDataArrayAccessor.sel_points` will
   now also return points that are located on the edges of 2D topologies.
 - :attr:`xugrid.Ugrid1d.dimensions` and :attr:`xugrid.Ugrid2d.dimensions` now
-  raise a FutureWarning; use ``.dims`` or ``.sizes`` instead.
+  give a FutureWarning; use ``.dims`` or ``.sizes`` instead.
 - Improved performance of :func:`xugrid.open_dataset` and
   :func:`xugrid.merge_partitions` when handling datasets with a large number
   of variables (>100).
@@ -827,4 +847,4 @@ Added
 ------------------
 
 .. _Keep a Changelog: https://keepachangelog.com/en/1.0.0/
-.. _Semantic Versioning: https://semver.org/spec/v2.0.0.html
+.. _Semantic Versioning: https://semver.org/spec/v2.0.0.html

tests/test_ugrid2d.py

@@ -1217,7 +1217,7 @@ def test_from_structured():
     assert grid.n_face == 4
 
 
-def test_form_structured_multicoord():
+def test_from_structured_multicoord():
     da = xr.DataArray(
         data=np.ones((2, 2)),
         coords={
@@ -1226,7 +1226,7 @@ def test_form_structured_multicoord():
         },
         dims=("y", "x"),
     )
-    grid = xugrid.Ugrid2d.from_structured_multicoord(da, x="xc", y="yc")
+    grid = xugrid.Ugrid2d._from_structured_multicoord(da, x="xc", y="yc")
     assert isinstance(grid, xugrid.Ugrid2d)
     assert grid.n_face == 4
 

tests/test_ugrid_dataset.py

@@ -162,47 +162,6 @@ def test_rename(self):
         renamed = self.uda.ugrid.rename("renamed")
         assert "renamed_nFaces" in renamed.dims
 
-    def test_from_structured(self):
-        da = xr.DataArray([0.0, 1.0, 2.0], {"x": [5.0, 10.0, 15.0]}, ["x"])
-        with pytest.raises(ValueError, match="Last two dimensions of da"):
-            xugrid.UgridDataArray.from_structured(da)
-
-        da = xr.DataArray(
-            data=np.arange(2 * 3 * 4).reshape((2, 3, 4)),
-            coords={"layer": [1, 2], "y": [5.0, 10.0, 15.0], "x": [2.0, 4.0, 6.0, 8.0]},
-            dims=["layer", "y", "x"],
-            name="grid",
-        )
-        uda = xugrid.UgridDataArray.from_structured(da)
-        assert isinstance(uda, xugrid.UgridDataArray)
-        assert uda.name == "grid"
-        assert uda.dims == ("layer", "mesh2d_nFaces")
-        assert uda.shape == (2, 12)
-        assert np.allclose(uda.ugrid.sel(x=2.0, y=5.0), [[0], [12]])
-        # Check whether flipping the y-axis doesn't cause any problems
-        flipped = da.isel(y=slice(None, None, -1))
-        uda = xugrid.UgridDataArray.from_structured(flipped)
-        assert np.allclose(uda.ugrid.sel(x=2.0, y=5.0), [[0], [12]])
-
-    def test_from_structured_multicoord(self):
-        da = xr.DataArray(
-            data=[[0, 1], [2, 3]],
-            coords={
-                "yc": (("y", "x"), [[12.0, 11.0], [12.0, 11.0]]),
-                "xc": (("y", "x"), [[10.0, 12.0], [10.0, 12.0]]),
-            },
-            dims=("y", "x"),
-        )
-        uda = xugrid.UgridDataArray.from_structured(da)
-        assert isinstance(uda, xugrid.UgridDataArray)
-        assert np.array_equal(np.unique(uda.ugrid.grid.node_x), [-0.5, 0.5, 1.5])
-        assert np.array_equal(uda.data, [0, 1, 2, 3])
-
-        uda = xugrid.UgridDataArray.from_structured(da, x="xc", y="yc")
-        assert isinstance(uda, xugrid.UgridDataArray)
-        assert np.array_equal(np.unique(uda.ugrid.grid.node_x), [9.0, 11.0, 13.0])
-        assert np.array_equal(uda.data, [0, 1, 2, 3])
-
     def test_unary_op(self):
         alltrue = self.uda.astype(bool)
         allfalse = alltrue.copy()
@@ -806,6 +765,113 @@ def test_reindex_like(self):
         assert isinstance(back, xugrid.UgridDataset)
 
 
+class TestFromStructured:
+    @pytest.fixture(autouse=True)
+    def setup(self):
+        self.da1d = xr.DataArray(
+            [0.0, 1.0, 2.0, 3.0], {"x": [2.0, 4.0, 6.0, 8.0]}, ["x"]
+        )
+        self.da2d = xr.DataArray(
+            data=np.arange(2 * 3 * 4).reshape((2, 3, 4)),
+            coords={"layer": [1, 2], "y": [5.0, 10.0, 15.0], "x": [2.0, 4.0, 6.0, 8.0]},
+            dims=["layer", "y", "x"],
+            name="grid",
+        )
+        self.da_coords2d = xr.DataArray(
+            data=[[0, 1], [2, 3]],
+            coords={
+                "yc": (("y", "x"), [[12.0, 11.0], [12.0, 11.0]]),
+                "xc": (("y", "x"), [[10.0, 12.0], [10.0, 12.0]]),
+            },
+            dims=("y", "x"),
+        )
+        self.ds = xr.Dataset(
+            {
+                "a": self.da2d,
+                "b": self.da1d,
+                "c": 1.0,
+            }
+        )
+
+    def test_error_1d(self):
+        with pytest.raises(
+            ValueError, match="DataArray must have at least two spatial dimensions"
+        ):
+            xugrid.UgridDataArray.from_structured(self.da1d)
+
+    def test_error_x_xor_y(self):
+        with pytest.raises(ValueError, match="Provide both x and y, or neither."):
+            xugrid.UgridDataArray.from_structured(self.da2d, x="this")
+
+    def test_missing_xy(self):
+        with pytest.raises(ValueError, match="Coordinates xc and yc are not present."):
+            xugrid.UgridDataArray.from_structured(self.da2d, x="xc", y="yc")
+
+    def test_from_dataarray(self):
+        uda = xugrid.UgridDataArray.from_structured(self.da2d)
+        assert isinstance(uda, xugrid.UgridDataArray)
+        assert uda.name == "grid"
+        assert uda.dims == ("layer", "mesh2d_nFaces")
+        assert uda.shape == (2, 12)
+        assert np.allclose(uda.ugrid.sel(x=2.0, y=5.0), [[0], [12]])
+        # Check whether flipping the y-axis doesn't cause any problems
+        flipped = self.da2d.isel(y=slice(None, None, -1))
+        uda = xugrid.UgridDataArray.from_structured(flipped)
+        assert np.allclose(uda.ugrid.sel(x=2.0, y=5.0), [[0], [12]])
+
+        # And test transposed.
+        daT = self.da2d.transpose()
+        uda = xugrid.UgridDataArray.from_structured(daT)
+        assert isinstance(uda, xugrid.UgridDataArray)
+        assert uda.name == "grid"
+        assert uda.dims == ("layer", "mesh2d_nFaces")
+        assert uda.shape == (2, 12)
+        assert np.allclose(uda.ugrid.sel(x=2.0, y=5.0), [[0], [12]])
+
+    def test_from_multicoord(self):
+        uda = xugrid.UgridDataArray.from_structured(self.da_coords2d)
+        assert isinstance(uda, xugrid.UgridDataArray)
+        assert np.array_equal(np.unique(uda.ugrid.grid.node_x), [-0.5, 0.5, 1.5])
+        assert np.array_equal(uda.data, [0, 1, 2, 3])
+
+        uda = xugrid.UgridDataArray.from_structured(self.da_coords2d, x="xc", y="yc")
+        assert isinstance(uda, xugrid.UgridDataArray)
+        assert np.array_equal(np.unique(uda.ugrid.grid.node_x), [9.0, 11.0, 13.0])
+        assert np.array_equal(uda.data, [0, 1, 2, 3])
+
+    def test_from_dataset(self):
+        uds = xugrid.UgridDataset.from_structured(self.ds)
+        assert isinstance(uds, xugrid.UgridDataset)
+        assert set(uds.data_vars) == {"a", "b", "c"}
+        assert uds["a"].dims == ("layer", "mesh2d_nFaces")
+        assert uds["b"].dims == ("x",)
+        assert uds["c"].dims == ()
+        uda = uds["a"]
+        assert uda.shape == (2, 12)
+        assert np.allclose(uda.ugrid.sel(x=2.0, y=5.0), [[0], [12]])
+
+    def test_from_multicoord_dataset(self):
+        ds = self.ds.copy()
+        da = self.da_coords2d.rename({"x": "x1", "y": "y1"})
+        ds["d"] = da
+        # Unspecified: it'll only infer x and y.
+        uds = xugrid.UgridDataset.from_structured(ds)
+        assert isinstance(uds, xugrid.UgridDataset)
+        assert uds["a"].dims == ("layer", "mesh2d_nFaces")
+        assert uds["d"].dims == ("y1", "x1")
+        assert len(uds.ugrid.grids) == 1
+        # Now specify separate topologies.
+        uds = xugrid.UgridDataset.from_structured(
+            ds, {"mesh2d_0": ("x", "y"), "mesh2d_1": ("xc", "yc")}
+        )
+        assert isinstance(uds, xugrid.UgridDataset)
+        assert uds["a"].dims == ("layer", "mesh2d_0_nFaces")
+        assert uds["b"].dims == ("x",)
+        assert uds["c"].dims == ()
+        assert uds["d"].dims == ("mesh2d_1_nFaces",)
+        assert len(uds.ugrid.grids) == 2
+
+
 def test_multiple_coordinates():
     grid = GRID()
     ds = UGRID_DS()

xugrid/core/wrap.py

@@ -243,14 +243,21 @@ def from_structured(
 
         The spatial dimensions are flattened into a single UGRID face dimension.
 
-        By default, this method looks for the "x" and "y" coordinates and assumes
-        they are one-dimensional. To convert rotated or curvilinear coordinates,
-        provide the names of the x and y coordinates.
+        By default, this method looks for:
+
+        1. ``"x"`` and ``"y"`` dimensions.
+        2. ``"longitude"`` and ``"latitude"`` dimensions.
+        3. ``"axis"`` attributes of "X" or "Y" on coordinates.
+        4. ``"standard_name"`` attributes of "longitude", "latitude",
+           "projection_x_coordinate", or "project_y_coordinate" on coordinate
+           variables.
+
+        Specify the x and y coordinate names explicitly otherwise.
 
         Parameters
         ----------
         da: xr.DataArray
-            Last two dimensions must be ``("y", "x")``.
+            Last two dimensions must be the y and x dimension (in that order!).
         x: str, default: None
             Which coordinate to use as the UGRID x-coordinate.
         y: str, default: None
@@ -260,30 +267,15 @@ def from_structured(
         -------
         unstructured: UgridDataArray
         """
-        if da.dims[-2:] != ("y", "x"):
-            raise ValueError('Last two dimensions of da must be ("y", "x")')
-        if (x is None) ^ (y is None):
-            raise ValueError("Provide both x and y, or neither.")
-        if x is None:
-            grid = Ugrid2d.from_structured(da)
-        else:
-            # Find out if it's multi-dimensional
-            xdim = da[x].ndim
-            if xdim == 1:
-                grid = Ugrid2d.from_structured(da, x=x, y=y)
-            elif xdim == 2:
-                grid = Ugrid2d.from_structured_multicoord(da, x=x, y=y)
-            else:
-                raise ValueError(f"x and y must be 1D or 2D. Found: {xdim}")
-
-        dims = da.dims[:-2]
-        coords = {k: da.coords[k] for k in dims}
-        face_da = xr.DataArray(
-            da.data.reshape(*da.shape[:-2], -1),
-            coords=coords,
-            dims=[*dims, grid.face_dimension],
-            name=da.name,
-        )
+        if da.ndim < 2:
+            raise ValueError(
+                "DataArray must have at least two spatial dimensions. "
+                f"Found: {da.dims}."
+            )
+        grid, stackdims = Ugrid2d.from_structured(da, x, y, return_dims=True)
+        face_da = da.stack(  # noqa: PD013
+            {grid.face_dimension: stackdims}, create_index=False
+        ).drop_vars(stackdims, errors="ignore")
         return UgridDataArray(face_da, grid)
 
     @staticmethod
@@ -421,3 +413,89 @@ def from_geodataframe(geodataframe: "geopandas.GeoDataFrame"):  # type: ignore #
         grid = grid_from_geodataframe(geodataframe)
         ds = xr.Dataset.from_dataframe(geodataframe.drop("geometry", axis=1))
         return UgridDataset(ds, [grid])
+
+    @staticmethod
+    def from_structured(
+        dataset: xr.Dataset, topology: dict | None = None
+    ) -> "UgridDataset":
+        """
+        Create a UgridDataset from a (structured) xarray Dataset.
+
+        The spatial dimensions are flattened into a single UGRID face dimension.
+
+        By default, this method looks for:
+
+        1. ``"x"`` and ``"y"`` dimensions.
+        2. ``"longitude"`` and ``"latitude"`` dimensions.
+        3. ``"axis"`` attributes of "X" or "Y" on coordinates.
+        4. ``"standard_name"`` attributes of "longitude", "latitude",
+           "projection_x_coordinate", or "project_y_coordinate" on coordinate
+           variables.
+
+        Specify the x and y coordinate names explicitly otherwise, see the
+        examples.
+
+        Parameters
+        ----------
+        dataset: xr.Dataset
+        topology: dict, optional, default is None.
+            Mapping of topology name to x and y coordinate variables.
+            If None, defaults to ``{"mesh2d": (None, None)}``.
+
+        Returns
+        -------
+        unstructured: UgridDataset
+
+        Examples
+        --------
+        By default, this method will look for ``"x"`` and ``"y"``
+        coordinates and returns a UgriDataset with a Ugrid topology named
+        mesh2d:
+
+        >>> uds = xugrid.UgridDataset.from_structured(dataset)
+
+        In case of other names, the name of the resulting UGRID topology and
+        the x and y coordinates must be specified:
+
+        >>> uds = xugrid.UgridDataset.from_structured(
+        >>>     dataset,
+        >>>     topology={"my_mesh2d": ("xc", "yc")},
+        >>> )
+
+        In case of multiple grid topologies in a single dataset, the names must
+        be specified as well:
+
+        >>> uds = xugrid.UgridDataset.from_structured(
+        >>>     dataset,
+        >>>     topology={"mesh2d_xy": ("x", "y"), "mesh2d_lonlat": {"lon", "lat"},
+        >>> )
+        """
+        if topology is None:
+            topology = {"mesh2d": (None, None)}
+
+        grids = []
+        dss = []
+        for name, (x, y) in topology.items():
+            grid, stackdims = Ugrid2d.from_structured(
+                dataset, x=x, y=y, name=name, return_dims=True
+            )
+            # Use subset to check that ALL dims of stackdims are present in the
+            # variable.
+            checkdims = set(stackdims)
+            ugrid_vars = [
+                name
+                for name, var in dataset.data_vars.items()
+                if checkdims.issubset(var.dims)
+            ]
+            dss.append(
+                dataset[ugrid_vars]  # noqa: PD013
+                .stack({grid.face_dimension: stackdims})
+                .drop_vars(stackdims + (grid.face_dimension,))
+            )
+            grids.append(grid)
+        # Add the original dataset to include all non-UGRID variables.
+        dss.append(dataset)
+        # Then merge with compat="override". This'll pick the first available
+        # variable: i.e. it will prioritize the UGRID form.
+        merged = xr.merge(dss, compat="override")
+        return UgridDataset(merged, grids)