add coordinate disambiguation with cf_xarray

docs/faq.rst

@@ -1,10 +1,10 @@
-Some common problems (and how to solve them)
-============================================
+FAQ
+===
 
 yt and xarray have many similarities in how they handle their Datasets, but
 there are also many aspects that differ to varying degree. This page describes
 some of the difficulties you may encounter while using yt_xarray to communicate
-between the two.
+between the two and how to solve those issues.
 
 xarray datasets with a mix of dimensionality
 ********************************************
@@ -26,7 +26,9 @@ yt datasets have a fixed expectation for coordinate names. In cartesian, these
 coordinate names are ``'x'``, ``'y'``, ``'z'`` while for geographic coordinate systems
 the coordinate names are ``'latitude'``, ``'longtiude'`` and then either ``'altitude'``
 or ``'depth'``. To work with xarray variables defined with coordinate names that
-differ from these, yt_xarray provides some coordinate aliasing.
+differ from these, yt_xarray provides some coordinate aliasing, which in part relies
+on `cf_xarray <https://cf-xarray.readthedocs.io>`_ (if it is installed) for
+additional conversion to standard names.
 
 See :doc:`examples/example_002_coord_aliases` for an example.
 

pyproject.toml

@@ -28,7 +28,7 @@ dependencies=['yt>=4.2.0', 'h5py>=3.4.0', 'pooch>=1.5.1', 'xarray']
 "Bug Tracker" = "https://github.com/data-exp-lab/yt_xarray/issues"
 
 [project.optional-dependencies]
-full = ["netCDF4", "scipy", "dask[complete]"]
+full = ["netCDF4", "scipy", "dask[complete]", "cf_xarray"]
 test = ["pytest", "pytest-cov", "cartopy"]
 docs = ["Sphinx==7.2.6", "jinja2==3.1.2", "nbsphinx==0.9.3"]
 

yt_xarray/__init__.py

@@ -8,5 +8,5 @@
 # import the xarray accessor so it is registered with xarray
 
 from .accessor import YtAccessor
-from .accessor._xr_to_yt import known_coord_aliases
+from .accessor._xr_to_yt import known_coord_aliases, reset_coordinate_aliases
 from .yt_xarray import open_dataset

yt_xarray/accessor/_xr_to_yt.py

@@ -1,5 +1,6 @@
 import collections.abc
 import enum
+from collections import defaultdict
 from typing import List, Optional, Tuple
 
 import numpy as np
@@ -57,7 +58,10 @@ def __init__(
         self.time_index_number: int = None
         self._process_selection(xr_ds)
 
-        self.yt_coord_names = _convert_to_yt_internal_coords(self.selected_coords)
+        xr_field = xr_ds.data_vars[fields[0]]
+        self.yt_coord_names = _convert_to_yt_internal_coords(
+            self.selected_coords, xr_field
+        )
 
     def _find_units(self, xr_ds) -> dict:
         units = {}
@@ -332,10 +336,26 @@ def interp_validation(self, geometry):
 }
 
 
-known_coord_aliases = {}
+_default_known_coord_aliases = {}
 for ky, vals in _coord_aliases.items():
     for val in vals:
-        known_coord_aliases[val] = ky
+        _default_known_coord_aliases[val] = ky
+
+known_coord_aliases = _default_known_coord_aliases.copy()
+
+
+def reset_coordinate_aliases():
+    kys_to_pop = [
+        ky
+        for ky in known_coord_aliases.keys()
+        if ky not in _default_known_coord_aliases
+    ]
+    for ky in kys_to_pop:
+        known_coord_aliases.pop(ky)
+
+    for ky, val in _default_known_coord_aliases.items():
+        known_coord_aliases[ky] = val
+
 
 _expected_yt_axes = {
     "cartesian": set(["x", "y", "z"]),
@@ -351,20 +371,55 @@ def interp_validation(self, geometry):
     _yt_coord_names += list(vals)
 
 
-def _convert_to_yt_internal_coords(coord_list):
+def _invert_cf_standard_names(standard_names: dict):
+    inverted_mapping = defaultdict(lambda: set())
+    for ky, vals in standard_names.items():
+        for val in vals:
+            inverted_mapping[val].add(ky)
+    return inverted_mapping
+
+
+def _cf_xr_coord_disamb(
+    cname: str, xr_field: xr.DataArray
+) -> Tuple[Optional[str], bool]:
+    # returns a tuple of (validated name, cf_xarray_is_installed)
+    try:
+        import cf_xarray as cfx  # noqa: F401
+    except ImportError:
+        return None, False
+
+    nm_to_standard = _invert_cf_standard_names(xr_field.cf.standard_names)
+    if cname in nm_to_standard:
+        cf_standard_name = nm_to_standard[cname]
+        if len(cf_standard_name):
+            cf_standard_name = list(cf_standard_name)[0]
+            if cf_standard_name in known_coord_aliases:
+                return cf_standard_name, True
+    return None, True
+
+
+def _convert_to_yt_internal_coords(coord_list: List[str], xr_field: xr.DataArray):
     yt_coords = []
     for c in coord_list:
         cname = c.lower()
+        cf_xarray_exists = None
         if cname in known_coord_aliases:
-            yt_coords.append(known_coord_aliases[cname])
+            valid_coord_name = known_coord_aliases[cname]
         elif cname in _yt_coord_names:
-            yt_coords.append(cname)
+            valid_coord_name = cname
         else:
-            raise ValueError(
+            valid_coord_name, cf_xarray_exists = _cf_xr_coord_disamb(cname, xr_field)
+        if valid_coord_name is None:
+            msg = (
                 f"{c} is not a known coordinate. To load in yt, you "
-                f"must supply an alias via the yt_xarray.known_coord_aliases"
-                f" dictionary."
+                "must supply an alias via the yt_xarray.known_coord_aliases"
+                " dictionary"
             )
+            if cf_xarray_exists is False:
+                msg += " or install cf_xarray to check for additional aliases."
+            raise ValueError(msg)
+
+        yt_coords.append(valid_coord_name)
 
     return yt_coords
 

yt_xarray/tests/test_xr_to_yt.py

@@ -1,3 +1,5 @@
+import builtins
+
 import numpy as np
 import pytest
 import xarray as xr
@@ -535,6 +537,43 @@ def test_reversed_axis(stretched, use_callable, chunksizes):
     assert np.all(np.isfinite(vals))
 
 
+def test_cf_xarray_disambiguation():
+    from cf_xarray.datasets import airds
+
+    # run the whole selection (will internally run coord disambiguation)
+    sel = xr2yt.Selection(
+        airds, fields=["air"], sel_dict={"time": 0}, sel_dict_type="isel"
+    )
+    xr_da = airds.air
+    selected_names = []
+    for c in sel.selected_coords:
+        selected_names.append(xr2yt._cf_xr_coord_disamb(c, xr_da)[0])
+
+    assert "latitude" in selected_names
+    assert "longitude" in selected_names
+
+
+def test_missing_cfxarray(monkeypatch):
+    from cf_xarray.datasets import airds
+
+    def _bad_import(name, globals=None, locals=None, fromlist=(), level=0):
+        raise ImportError
+
+    xr_da = airds.air
+    clist = list(xr_da.dims)
+    with monkeypatch.context() as m:
+        m.setattr(builtins, "__import__", _bad_import)
+        with pytest.raises(ValueError, match=f"{clist[0]} is not"):
+
+            _ = xr2yt._convert_to_yt_internal_coords(clist, xr_da)
+
+
+def test_coord_alias_reset():
+    xr2yt.known_coord_aliases["blah"] = "lwkerj"
+    xr2yt.reset_coordinate_aliases()
+    assert "blah" not in xr2yt.known_coord_aliases
+
+
 def test_reader_with_2d_space_time_and_reverse_axis():
 
     # test for https://github.com/data-exp-lab/yt_xarray/issues/86