Hierarchical coordinates in DataTree (#9063)

* Inheritance of data coordinates

* Simplify __init__

* Include path name in alignment errors

* Fix some mypy errors

* mypy fix

* simplify DataTree data model

* Add to_dataset(local=True)

* Fix mypy failure in tests

* Fix to_zarr for inherited coords

* Fix to_netcdf for heirarchical coords

* Add ChainSet

* Revise internal data model; remove ChainSet

* add another way to construct inherited indexes

* Finish refactoring error message

* include inherited dimensions in HTML repr, too

* Construct ChainMap objects on demand.

* slightly better error message with mis-aligned data trees

* mypy fix

* use float64 instead of float32 for windows

* clean-up per review

* Add note about inheritance to .ds docs

xarray/core/datatree_io.py

@@ -85,7 +85,7 @@ def _datatree_to_netcdf(
         unlimited_dims = {}
 
     for node in dt.subtree:
-        ds = node.ds
+        ds = node.to_dataset(inherited=False)
         group_path = node.path
         if ds is None:
             _create_empty_netcdf_group(filepath, group_path, mode, engine)
@@ -151,7 +151,7 @@ def _datatree_to_zarr(
         )
 
     for node in dt.subtree:
-        ds = node.ds
+        ds = node.to_dataset(inherited=False)
         group_path = node.path
         if ds is None:
             _create_empty_zarr_group(store, group_path, mode)

xarray/core/formatting.py

@@ -748,6 +748,27 @@ def dataset_repr(ds):
     return "\n".join(summary)
 
 
+def dims_and_coords_repr(ds) -> str:
+    """Partial Dataset repr for use inside DataTree inheritance errors."""
+    summary = []
+
+    col_width = _calculate_col_width(ds.coords)
+    max_rows = OPTIONS["display_max_rows"]
+
+    dims_start = pretty_print("Dimensions:", col_width)
+    dims_values = dim_summary_limited(ds, col_width=col_width + 1, max_rows=max_rows)
+    summary.append(f"{dims_start}({dims_values})")
+
+    if ds.coords:
+        summary.append(coords_repr(ds.coords, col_width=col_width, max_rows=max_rows))
+
+    unindexed_dims_str = unindexed_dims_repr(ds.dims, ds.coords, max_rows=max_rows)
+    if unindexed_dims_str:
+        summary.append(unindexed_dims_str)
+
+    return "\n".join(summary)
+
+
 def diff_dim_summary(a, b):
     if a.sizes != b.sizes:
         return f"Differing dimensions:\n    ({dim_summary(a)}) != ({dim_summary(b)})"
@@ -1030,7 +1051,7 @@ def diff_datatree_repr(a: DataTree, b: DataTree, compat):
 def _single_node_repr(node: DataTree) -> str:
     """Information about this node, not including its relationships to other nodes."""
     if node.has_data or node.has_attrs:
-        ds_info = "\n" + repr(node.ds)
+        ds_info = "\n" + repr(node._to_dataset_view(rebuild_dims=False))
     else:
         ds_info = ""
     return f"Group: {node.path}{ds_info}"

xarray/core/formatting_html.py

@@ -386,7 +386,7 @@ def summarize_datatree_children(children: Mapping[str, DataTree]) -> str:
 def datatree_node_repr(group_title: str, dt: DataTree) -> str:
     header_components = [f"<div class='xr-obj-type'>{escape(group_title)}</div>"]
 
-    ds = dt.ds
+    ds = dt._to_dataset_view(rebuild_dims=False)
 
     sections = [
         children_section(dt.children),

xarray/core/treenode.py

@@ -138,14 +138,14 @@ def _attach(self, parent: Tree | None, child_name: str | None = None) -> None:
                     "To directly set parent, child needs a name, but child is unnamed"
                 )
 
-            self._pre_attach(parent)
+            self._pre_attach(parent, child_name)
             parentchildren = parent._children
             assert not any(
                 child is self for child in parentchildren
             ), "Tree is corrupt."
             parentchildren[child_name] = self
             self._parent = parent
-            self._post_attach(parent)
+            self._post_attach(parent, child_name)
         else:
             self._parent = None
 
@@ -415,11 +415,11 @@ def _post_detach(self: Tree, parent: Tree) -> None:
         """Method call after detaching from `parent`."""
         pass
 
-    def _pre_attach(self: Tree, parent: Tree) -> None:
+    def _pre_attach(self: Tree, parent: Tree, name: str) -> None:
         """Method call before attaching to `parent`."""
         pass
 
-    def _post_attach(self: Tree, parent: Tree) -> None:
+    def _post_attach(self: Tree, parent: Tree, name: str) -> None:
         """Method call after attaching to `parent`."""
         pass
 
@@ -567,6 +567,9 @@ def same_tree(self, other: Tree) -> bool:
         return self.root is other.root
 
 
+AnyNamedNode = TypeVar("AnyNamedNode", bound="NamedNode")
+
+
 class NamedNode(TreeNode, Generic[Tree]):
     """
     A TreeNode which knows its own name.
@@ -606,10 +609,9 @@ def __repr__(self, level=0):
     def __str__(self) -> str:
         return f"NamedNode('{self.name}')" if self.name else "NamedNode()"
 
-    def _post_attach(self: NamedNode, parent: NamedNode) -> None:
+    def _post_attach(self: AnyNamedNode, parent: AnyNamedNode, name: str) -> None:
         """Ensures child has name attribute corresponding to key under which it has been stored."""
-        key = next(k for k, v in parent.children.items() if v is self)
-        self.name = key
+        self.name = name
 
     @property
     def path(self) -> str:

xarray/tests/test_backends_datatree.py

@@ -1,10 +1,12 @@
 from __future__ import annotations
 
-from typing import TYPE_CHECKING
+from typing import TYPE_CHECKING, cast
 
 import pytest
 
+import xarray as xr
 from xarray.backends.api import open_datatree
+from xarray.core.datatree import DataTree
 from xarray.testing import assert_equal
 from xarray.tests import (
     requires_h5netcdf,
@@ -13,11 +15,11 @@
 )
 
 if TYPE_CHECKING:
-    from xarray.backends.api import T_NetcdfEngine
+    from xarray.core.datatree_io import T_DataTreeNetcdfEngine
 
 
 class DatatreeIOBase:
-    engine: T_NetcdfEngine | None = None
+    engine: T_DataTreeNetcdfEngine | None = None
 
     def test_to_netcdf(self, tmpdir, simple_datatree):
         filepath = tmpdir / "test.nc"
@@ -27,6 +29,21 @@ def test_to_netcdf(self, tmpdir, simple_datatree):
         roundtrip_dt = open_datatree(filepath, engine=self.engine)
         assert_equal(original_dt, roundtrip_dt)
 
+    def test_to_netcdf_inherited_coords(self, tmpdir):
+        filepath = tmpdir / "test.nc"
+        original_dt = DataTree.from_dict(
+            {
+                "/": xr.Dataset({"a": (("x",), [1, 2])}, coords={"x": [3, 4]}),
+                "/sub": xr.Dataset({"b": (("x",), [5, 6])}),
+            }
+        )
+        original_dt.to_netcdf(filepath, engine=self.engine)
+
+        roundtrip_dt = open_datatree(filepath, engine=self.engine)
+        assert_equal(original_dt, roundtrip_dt)
+        subtree = cast(DataTree, roundtrip_dt["/sub"])
+        assert "x" not in subtree.to_dataset(inherited=False).coords
+
     def test_netcdf_encoding(self, tmpdir, simple_datatree):
         filepath = tmpdir / "test.nc"
         original_dt = simple_datatree
@@ -48,12 +65,12 @@ def test_netcdf_encoding(self, tmpdir, simple_datatree):
 
 @requires_netCDF4
 class TestNetCDF4DatatreeIO(DatatreeIOBase):
-    engine: T_NetcdfEngine | None = "netcdf4"
+    engine: T_DataTreeNetcdfEngine | None = "netcdf4"
 
 
 @requires_h5netcdf
 class TestH5NetCDFDatatreeIO(DatatreeIOBase):
-    engine: T_NetcdfEngine | None = "h5netcdf"
+    engine: T_DataTreeNetcdfEngine | None = "h5netcdf"
 
 
 @requires_zarr
@@ -119,3 +136,18 @@ def test_to_zarr_default_write_mode(self, tmpdir, simple_datatree):
         # with default settings, to_zarr should not overwrite an existing dir
         with pytest.raises(zarr.errors.ContainsGroupError):
             simple_datatree.to_zarr(tmpdir)
+
+    def test_to_zarr_inherited_coords(self, tmpdir):
+        original_dt = DataTree.from_dict(
+            {
+                "/": xr.Dataset({"a": (("x",), [1, 2])}, coords={"x": [3, 4]}),
+                "/sub": xr.Dataset({"b": (("x",), [5, 6])}),
+            }
+        )
+        filepath = tmpdir / "test.zarr"
+        original_dt.to_zarr(filepath)
+
+        roundtrip_dt = open_datatree(filepath, engine="zarr")
+        assert_equal(original_dt, roundtrip_dt)
+        subtree = cast(DataTree, roundtrip_dt["/sub"])
+        assert "x" not in subtree.to_dataset(inherited=False).coords