Automatically choose x,y for plots

cf_xarray/accessor.py

@@ -655,6 +655,42 @@ def check_results(names, k):
         )
 
 
+def _possible_x_y_plot(obj, key):
+    """Guesses a name for an x/y variable if possible."""
+    # in priority order
+    x_criteria = [
+        ("coordinates", "longitude"),
+        ("axes", "X"),
+        ("coordinates", "time"),
+        ("axes", "T"),
+    ]
+    y_criteria = [
+        ("coordinates", "vertical"),
+        ("axes", "Z"),
+        ("coordinates", "latitude"),
+        ("axes", "Y"),
+    ]
+
+    def _get_possible(accessor, criteria):
+        # is_scalar depends on NON_NUMPY_SUPPORTED_TYPES
+        # importing a private function seems better than
+        # maintaining that variable!
+        from xarray.core.utils import is_scalar
+
+        for attr, key in criteria:
+            value = getattr(accessor, attr).get(key)
+            if not value or len(value) > 1:
+                continue
+            if not is_scalar(accessor._obj[value[0]]):
+                return value[0]
+        return None
+
+    if key == "x":
+        return _get_possible(obj.cf, x_criteria)
+    elif key == "y":
+        return _get_possible(obj.cf, y_criteria)
+
+
 class _CFWrappedClass:
     """
     This class is used to wrap any class in _WRAPPED_CLASSES.
@@ -705,27 +741,34 @@ def _plot_decorator(self, func):
 
         @functools.wraps(func)
         def _plot_wrapper(*args, **kwargs):
-            if "x" in kwargs:
-                if kwargs["x"] in valid_keys:
-                    xvar = self.accessor[kwargs["x"]]
-                else:
-                    xvar = self._obj[kwargs["x"]]
-                if "positive" in xvar.attrs:
-                    if xvar.attrs["positive"] == "down":
-                        kwargs.setdefault("xincrease", False)
-                    else:
-                        kwargs.setdefault("xincrease", True)
+            def _process_x_or_y(kwargs, key):
+                if key not in kwargs:
+                    kwargs[key] = _possible_x_y_plot(self._obj, key)
 
-            if "y" in kwargs:
-                if kwargs["y"] in valid_keys:
-                    yvar = self.accessor[kwargs["y"]]
-                else:
-                    yvar = self._obj[kwargs["y"]]
-                if "positive" in yvar.attrs:
-                    if yvar.attrs["positive"] == "down":
-                        kwargs.setdefault("yincrease", False)
+                value = kwargs.get(key)
+                if value:
+                    if value in valid_keys:
+                        var = self.accessor[value]
                     else:
-                        kwargs.setdefault("yincrease", True)
+                        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
+
+            is_line_plot = (func.__name__ == "line") or (
+                func.__name__ == "wrapper" and kwargs.get("hue")
+            )
+            if is_line_plot:
+                if not kwargs.get("hue"):
+                    kwargs = _process_x_or_y(kwargs, "x")
+                    if not kwargs.get("x"):
+                        kwargs = _process_x_or_y(kwargs, "y")
+            else:
+                kwargs = _process_x_or_y(kwargs, "x")
+                kwargs = _process_x_or_y(kwargs, "y")
 
             return func(*args, **kwargs)
 

cf_xarray/tests/test_accessor.py

@@ -293,15 +293,20 @@ def test_dataarray_getitem():
     assert_identical(air.cf["area_grid_cell"], air.cell_area.reset_coords(drop=True))
 
 
-@pytest.mark.parametrize("obj", dataarrays)
-def test_dataarray_plot(obj):
+def test_dataarray_plot():
+
+    obj = airds.air
 
-    rv = obj.isel(time=1).cf.plot(x="X", y="Y")
+    rv = obj.isel(time=1).transpose("lon", "lat").cf.plot()
     assert isinstance(rv, mpl.collections.QuadMesh)
+    assert all(v > 180 for v in rv.axes.get_xlim())
+    assert all(v < 200 for v in rv.axes.get_ylim())
     plt.close()
 
-    rv = obj.isel(time=1).cf.plot.contourf(x="X", y="Y")
+    rv = obj.isel(time=1).transpose("lon", "lat").cf.plot.contourf()
     assert isinstance(rv, mpl.contour.QuadContourSet)
+    assert all(v > 180 for v in rv.axes.get_xlim())
+    assert all(v < 200 for v in rv.axes.get_ylim())
     plt.close()
 
     rv = obj.cf.plot(x="X", y="Y", col="T")
@@ -316,6 +321,29 @@ def test_dataarray_plot(obj):
     assert all([isinstance(line, mpl.lines.Line2D) for line in rv])
     plt.close()
 
+    # set y automatically
+    rv = obj.isel(time=0, lon=1).cf.plot.line()
+    np.testing.assert_equal(rv[0].get_ydata(), obj.lat.data)
+    plt.close()
+
+    # don't set y automatically
+    rv = obj.isel(time=0, lon=1).cf.plot.line(x="lat")
+    np.testing.assert_equal(rv[0].get_xdata(), obj.lat.data)
+    plt.close()
+
+    # various line plots and automatic guessing
+    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()
+
+    # 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)
+    # plt.close()
+
+    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")
@@ -714,3 +742,34 @@ def test_drop_dims(ds):
     # Axis and coordinate
     for cf_name in ["X", "longitude"]:
         assert_identical(ds.drop_dims("lon"), ds.cf.drop_dims(cf_name))
+
+
+def test_possible_x_y_plot():
+    from ..accessor import _possible_x_y_plot
+
+    # choose axes
+    assert _possible_x_y_plot(airds.air.isel(time=1), "x") == "lon"
+    assert _possible_x_y_plot(airds.air.isel(time=1), "y") == "lat"
+    assert _possible_x_y_plot(airds.air.isel(lon=1), "y") == "lat"
+    assert _possible_x_y_plot(airds.air.isel(lon=1), "x") == "time"
+
+    # choose coordinates over axes
+    assert _possible_x_y_plot(popds.UVEL, "x") == "ULONG"
+    assert _possible_x_y_plot(popds.UVEL, "y") == "ULAT"
+    assert _possible_x_y_plot(popds.TEMP, "x") == "TLONG"
+    assert _possible_x_y_plot(popds.TEMP, "y") == "TLAT"
+
+    assert _possible_x_y_plot(popds.UVEL.drop_vars("ULONG"), "x") == "nlon"
+
+    # choose X over T, Y over Z
+    def makeds(*dims):
+        coords = {dim: (dim, np.arange(3), {"axis": dim}) for dim in dims}
+        return xr.DataArray(np.zeros((3, 3)), dims=dims, coords=coords)
+
+    yzds = makeds("Y", "Z")
+    assert _possible_x_y_plot(yzds, "y") == "Z"
+    assert _possible_x_y_plot(yzds, "x") is None
+
+    xtds = makeds("X", "T")
+    assert _possible_x_y_plot(xtds, "y") is None
+    assert _possible_x_y_plot(xtds, "x") == "X"

doc/whats-new.rst

@@ -6,6 +6,7 @@ What's New
 v0.4.1 (unreleased)
 ===================
 
+- Automatically set ``x`` or ``y`` for :py:attr:`DataArray.cf.plot`. By `Deepak Cherian`_.
 - Added scripts to document :ref:`criteria` with tables. By `Mattia Almansi`_.
 - Support for ``.drop()``, ``.drop_vars()``, ``.drop_sel()``, ``.drop_dims()``, ``.set_coords()``, ``.reset_coords()``. By `Mattia Almansi`_.
 - Support for using ``standard_name`` in more functions. (:pr:`128`) By `Deepak Cherian`_