Avoid setting 1D x,y where that dimension clashes with hue. (#298)

cf_xarray/accessor.py

@@ -765,7 +765,15 @@ def _get_possible(accessor, criteria):
             elif ax_coord_name:
                 values = [v for v in values if v in ax_coord_name]
 
-            values = [v for v in values if v != skip]
+            if skip is not None:
+                skipvar = obj.cf[skip]
+                bad_names = (skip, skipvar.name)
+                bad_dims = ((skip,), skipvar.dims)
+                values = [
+                    v
+                    for v in values
+                    if v not in bad_names and obj[v].dims not in bad_dims
+                ]
             if len(values) == 1 and not is_scalar(accessor._obj[values[0]]):
                 return values[0]
             else:

cf_xarray/tests/test_accessor.py

@@ -1223,6 +1223,14 @@ def makeds(*dims):
     assert _possible_x_y_plot(xtds, "y") is None
     assert _possible_x_y_plot(xtds, "x") == "X"
 
+    xtds.coords["lon"] = ("X", [1, 2, 3], {"standard_name": "longitude"})
+    # skip lon (which is 1D on X) if user passes hue="X"
+    # choose T instead which is a different dimension
+    # (and so a more meaningful plot)
+    assert _possible_x_y_plot(xtds, "x", skip="X") == "T"
+    # now with hue="lon", skip "X"
+    assert _possible_x_y_plot(xtds, "x", skip="lon") == "T"
+
 
 def test_groupby_special_ops():
     cfgrouped = airds.cf.groupby_bins("latitude", np.arange(20, 50, 10))