Use concise date format when plotting (#8449)

* Add concise date format

* Update utils.py

* Update dataarray_plot.py

* Update dataarray_plot.py

* Update whats-new.rst

* Cleanup

* Clarify xfail reason

* Update whats-new.rst

Author: Illviljan

doc/whats-new.rst

@@ -23,6 +23,8 @@ v2023.11.1 (unreleased)
 New Features
 ~~~~~~~~~~~~
 
+- Use a concise format when plotting datetime arrays. (:pull:`8449`).
+  By `Jimmy Westling <https://github.com/illviljan>`_.
 
 Breaking changes
 ~~~~~~~~~~~~~~~~

xarray/plot/dataarray_plot.py

@@ -27,6 +27,7 @@
     _rescale_imshow_rgb,
     _resolve_intervals_1dplot,
     _resolve_intervals_2dplot,
+    _set_concise_date,
     _update_axes,
     get_axis,
     label_from_attrs,
@@ -525,14 +526,8 @@ def line(
         assert hueplt is not None
         ax.legend(handles=primitive, labels=list(hueplt.to_numpy()), title=hue_label)
 
-    # Rotate dates on xlabels
-    # Do this without calling autofmt_xdate so that x-axes ticks
-    # on other subplots (if any) are not deleted.
-    # https://stackoverflow.com/questions/17430105/autofmt-xdate-deletes-x-axis-labels-of-all-subplots
     if np.issubdtype(xplt.dtype, np.datetime64):
-        for xlabels in ax.get_xticklabels():
-            xlabels.set_rotation(30)
-            xlabels.set_horizontalalignment("right")
+        _set_concise_date(ax, axis="x")
 
     _update_axes(ax, xincrease, yincrease, xscale, yscale, xticks, yticks, xlim, ylim)
 
@@ -1087,14 +1082,12 @@ def _add_labels(
     add_labels: bool | Iterable[bool],
     darrays: Iterable[DataArray | None],
     suffixes: Iterable[str],
-    rotate_labels: Iterable[bool],
     ax: Axes,
 ) -> None:
     """Set x, y, z labels."""
     add_labels = [add_labels] * 3 if isinstance(add_labels, bool) else add_labels
-    for axis, add_label, darray, suffix, rotate_label in zip(
-        ("x", "y", "z"), add_labels, darrays, suffixes, rotate_labels
-    ):
+    axes: tuple[Literal["x", "y", "z"], ...] = ("x", "y", "z")
+    for axis, add_label, darray, suffix in zip(axes, add_labels, darrays, suffixes):
         if darray is None:
             continue
 
@@ -1103,14 +1096,8 @@ def _add_labels(
             if label is not None:
                 getattr(ax, f"set_{axis}label")(label)
 
-        if rotate_label and np.issubdtype(darray.dtype, np.datetime64):
-            # Rotate dates on xlabels
-            # Do this without calling autofmt_xdate so that x-axes ticks
-            # on other subplots (if any) are not deleted.
-            # https://stackoverflow.com/questions/17430105/autofmt-xdate-deletes-x-axis-labels-of-all-subplots
-            for labels in getattr(ax, f"get_{axis}ticklabels")():
-                labels.set_rotation(30)
-                labels.set_horizontalalignment("right")
+        if np.issubdtype(darray.dtype, np.datetime64):
+            _set_concise_date(ax, axis=axis)
 
 
 @overload
@@ -1265,7 +1252,7 @@ def scatter(
         kwargs.update(s=sizeplt.to_numpy().ravel())
 
     plts_or_none = (xplt, yplt, zplt)
-    _add_labels(add_labels, plts_or_none, ("", "", ""), (True, False, False), ax)
+    _add_labels(add_labels, plts_or_none, ("", "", ""), ax)
 
     xplt_np = None if xplt is None else xplt.to_numpy().ravel()
     yplt_np = None if yplt is None else yplt.to_numpy().ravel()
@@ -1653,14 +1640,8 @@ def newplotfunc(
             ax, xincrease, yincrease, xscale, yscale, xticks, yticks, xlim, ylim
         )
 
-        # Rotate dates on xlabels
-        # Do this without calling autofmt_xdate so that x-axes ticks
-        # on other subplots (if any) are not deleted.
-        # https://stackoverflow.com/questions/17430105/autofmt-xdate-deletes-x-axis-labels-of-all-subplots
         if np.issubdtype(xplt.dtype, np.datetime64):
-            for xlabels in ax.get_xticklabels():
-                xlabels.set_rotation(30)
-                xlabels.set_horizontalalignment("right")
+            _set_concise_date(ax, "x")
 
         return primitive
 

xarray/plot/utils.py

@@ -6,7 +6,7 @@
 from collections.abc import Hashable, Iterable, Mapping, MutableMapping, Sequence
 from datetime import datetime
 from inspect import getfullargspec
-from typing import TYPE_CHECKING, Any, Callable, overload
+from typing import TYPE_CHECKING, Any, Callable, Literal, overload
 
 import numpy as np
 import pandas as pd
@@ -1827,3 +1827,27 @@ def _guess_coords_to_plot(
         _assert_valid_xy(darray, dim, k)
 
     return coords_to_plot
+
+
+def _set_concise_date(ax: Axes, axis: Literal["x", "y", "z"] = "x") -> None:
+    """
+    Use ConciseDateFormatter which is meant to improve the
+    strings chosen for the ticklabels, and to minimize the
+    strings used in those tick labels as much as possible.
+
+    https://matplotlib.org/stable/gallery/ticks/date_concise_formatter.html
+
+    Parameters
+    ----------
+    ax : Axes
+        Figure axes.
+    axis : Literal["x", "y", "z"], optional
+        Which axis to make concise. The default is "x".
+    """
+    import matplotlib.dates as mdates
+
+    locator = mdates.AutoDateLocator()
+    formatter = mdates.ConciseDateFormatter(locator)
+    _axis = getattr(ax, f"{axis}axis")
+    _axis.set_major_locator(locator)
+    _axis.set_major_formatter(formatter)

xarray/tests/test_plot.py

@@ -787,12 +787,17 @@ def test_plot_nans(self) -> None:
         self.darray[1] = np.nan
         self.darray.plot.line()
 
-    def test_x_ticks_are_rotated_for_time(self) -> None:
+    def test_dates_are_concise(self) -> None:
+        import matplotlib.dates as mdates
+
         time = pd.date_range("2000-01-01", "2000-01-10")
         a = DataArray(np.arange(len(time)), [("t", time)])
         a.plot.line()
-        rotation = plt.gca().get_xticklabels()[0].get_rotation()
-        assert rotation != 0
+
+        ax = plt.gca()
+
+        assert isinstance(ax.xaxis.get_major_locator(), mdates.AutoDateLocator)
+        assert isinstance(ax.xaxis.get_major_formatter(), mdates.ConciseDateFormatter)
 
     def test_xyincrease_false_changes_axes(self) -> None:
         self.darray.plot.line(xincrease=False, yincrease=False)
@@ -1356,12 +1361,17 @@ def test_xyincrease_true_changes_axes(self) -> None:
         diffs = xlim[0] - 0, xlim[1] - 14, ylim[0] - 0, ylim[1] - 9
         assert all(abs(x) < 1 for x in diffs)
 
-    def test_x_ticks_are_rotated_for_time(self) -> None:
+    def test_dates_are_concise(self) -> None:
+        import matplotlib.dates as mdates
+
         time = pd.date_range("2000-01-01", "2000-01-10")
         a = DataArray(np.random.randn(2, len(time)), [("xx", [1, 2]), ("t", time)])
-        a.plot(x="t")
-        rotation = plt.gca().get_xticklabels()[0].get_rotation()
-        assert rotation != 0
+        self.plotfunc(a, x="t")
+
+        ax = plt.gca()
+
+        assert isinstance(ax.xaxis.get_major_locator(), mdates.AutoDateLocator)
+        assert isinstance(ax.xaxis.get_major_formatter(), mdates.ConciseDateFormatter)
 
     def test_plot_nans(self) -> None:
         x1 = self.darray[:5]
@@ -1888,6 +1898,25 @@ def test_interval_breaks_logspace(self) -> None:
 class TestImshow(Common2dMixin, PlotTestCase):
     plotfunc = staticmethod(xplt.imshow)
 
+    @pytest.mark.xfail(
+        reason=(
+            "Failing inside matplotlib. Should probably be fixed upstream because "
+            "other plot functions can handle it. "
+            "Remove this test when it works, already in Common2dMixin"
+        )
+    )
+    def test_dates_are_concise(self) -> None:
+        import matplotlib.dates as mdates
+
+        time = pd.date_range("2000-01-01", "2000-01-10")
+        a = DataArray(np.random.randn(2, len(time)), [("xx", [1, 2]), ("t", time)])
+        self.plotfunc(a, x="t")
+
+        ax = plt.gca()
+
+        assert isinstance(ax.xaxis.get_major_locator(), mdates.AutoDateLocator)
+        assert isinstance(ax.xaxis.get_major_formatter(), mdates.ConciseDateFormatter)
+
     @pytest.mark.slow
     def test_imshow_called(self) -> None:
         # Having both statements ensures the test works properly
@@ -2032,6 +2061,25 @@ class TestSurface(Common2dMixin, PlotTestCase):
     plotfunc = staticmethod(xplt.surface)
     subplot_kws = {"projection": "3d"}
 
+    @pytest.mark.xfail(
+        reason=(
+            "Failing inside matplotlib. Should probably be fixed upstream because "
+            "other plot functions can handle it. "
+            "Remove this test when it works, already in Common2dMixin"
+        )
+    )
+    def test_dates_are_concise(self) -> None:
+        import matplotlib.dates as mdates
+
+        time = pd.date_range("2000-01-01", "2000-01-10")
+        a = DataArray(np.random.randn(2, len(time)), [("xx", [1, 2]), ("t", time)])
+        self.plotfunc(a, x="t")
+
+        ax = plt.gca()
+
+        assert isinstance(ax.xaxis.get_major_locator(), mdates.AutoDateLocator)
+        assert isinstance(ax.xaxis.get_major_formatter(), mdates.ConciseDateFormatter)
+
     def test_primitive_artist_returned(self) -> None:
         artist = self.plotmethod()
         assert isinstance(artist, mpl_toolkits.mplot3d.art3d.Poly3DCollection)