Set xincrease/yincrease in more cases. (#287)

Author: dcherian

cf_xarray/accessor.py

@@ -822,48 +822,54 @@ def __init__(self, obj, accessor):
         self.accessor = accessor
         self._keys = ("x", "y", "hue", "col", "row")
 
+    def _process_x_or_y(self, kwargs, key, skip=None):
+        """Choose a default 'x' or 'y' variable name."""
+        if key not in kwargs:
+            kwargs[key] = _possible_x_y_plot(self._obj, key, skip)
+        return kwargs
+
+    def _set_axis_props(self, kwargs, key):
+        value = kwargs.get(key)
+        if value:
+            if value in self.accessor.keys():
+                var = self.accessor[value]
+            else:
+                var = self._obj[value]
+            if "positive" in var.attrs:
+                if var.attrs["positive"] == "down":
+                    kwargs.setdefault(f"{key}increase", False)
+                else:
+                    kwargs.setdefault(f"{key}increase", True)
+        return kwargs
+
     def _plot_decorator(self, func):
         """
         This decorator is used to set default kwargs on plotting functions.
         For now, this can
         1. set ``xincrease`` and ``yincrease``.
         2. automatically set ``x`` or ``y``.
         """
-        valid_keys = self.accessor.keys()
 
         @functools.wraps(func)
         def _plot_wrapper(*args, **kwargs):
-            def _process_x_or_y(kwargs, key, skip=None):
-                if key not in kwargs:
-                    kwargs[key] = _possible_x_y_plot(self._obj, key, skip)
-
-                value = kwargs.get(key)
-                if value:
-                    if value in valid_keys:
-                        var = self.accessor[value]
-                    else:
-                        var = self._obj[value]
-                    if "positive" in var.attrs:
-                        if var.attrs["positive"] == "down":
-                            kwargs.setdefault(f"{key}increase", False)
-                        else:
-                            kwargs.setdefault(f"{key}increase", True)
-                return kwargs
-
+            # First choose 'x' or 'y' if possible
             is_line_plot = (func.__name__ == "line") or (
                 func.__name__ == "wrapper"
                 and (kwargs.get("hue") or self._obj.ndim == 1)
             )
             if is_line_plot:
                 hue = kwargs.get("hue")
                 if "x" not in kwargs and "y" not in kwargs:
-                    kwargs = _process_x_or_y(kwargs, "x", skip=hue)
+                    kwargs = self._process_x_or_y(kwargs, "x", skip=hue)
                     if not kwargs.get("x"):
-                        kwargs = _process_x_or_y(kwargs, "y", skip=hue)
-
+                        kwargs = self._process_x_or_y(kwargs, "y", skip=hue)
             else:
-                kwargs = _process_x_or_y(kwargs, "x", skip=kwargs.get("y"))
-                kwargs = _process_x_or_y(kwargs, "y", skip=kwargs.get("x"))
+                kwargs = self._process_x_or_y(kwargs, "x", skip=kwargs.get("y"))
+                kwargs = self._process_x_or_y(kwargs, "y", skip=kwargs.get("x"))
+
+            # Now set some nice properties
+            kwargs = self._set_axis_props(kwargs, "x")
+            kwargs = self._set_axis_props(kwargs, "y")
 
             return func(*args, **kwargs)
 

cf_xarray/tests/test_accessor.py

@@ -509,7 +509,7 @@ def test_dataarray_getitem():
 
 def test_dataarray_plot():
 
-    obj = airds.air
+    obj = airds.air.copy(deep=True)
 
     rv = obj.isel(time=1).transpose("lon", "lat").cf.plot()
     assert isinstance(rv, mpl.collections.QuadMesh)
@@ -554,15 +554,18 @@ def test_dataarray_plot():
     np.testing.assert_equal(rv[0].get_xdata(), obj.lon.data)
     plt.close()
 
+    obj.lon.attrs["positive"] = "down"
     rv = obj.cf.isel(T=1, Y=[0, 1, 2]).cf.plot(hue="Y")
     np.testing.assert_equal(rv[0].get_xdata(), obj.lon.data)
+    xlim = rv[0].axes.get_xlim()
+    assert xlim[0] > xlim[1]
     plt.close()
+    del obj.lon.attrs["positive"]
 
     rv = obj.cf.isel(T=1, Y=[0, 1, 2]).cf.plot.line()
     np.testing.assert_equal(rv[0].get_xdata(), obj.lon.data)
     plt.close()
 
-    obj = obj.copy(deep=True)
     obj.time.attrs.clear()
     rv = obj.cf.plot(x="X", y="Y", col="time")
     assert isinstance(rv, xr.plot.FacetGrid)