Fix datetime in colorbar

xarray/plot/dataarray_plot.py

@@ -1029,6 +1029,9 @@ def newplotfunc(
             if "label" not in cbar_kwargs:
                 cbar_kwargs["label"] = label_from_attrs(hueplt_norm.data)
 
+            if np.issubdtype(hueplt_norm.data.dtype, np.datetime64):
+                cbar_kwargs["_use_concise_date"] = True
+
             _add_colorbar(
                 primitive, ax, kwargs.get("cbar_ax", None), cbar_kwargs, cmap_params
             )

xarray/plot/utils.py

@@ -710,6 +710,8 @@ def _is_numeric(arr):
 
 
 def _add_colorbar(primitive, ax, cbar_ax, cbar_kwargs, cmap_params):
+    _use_concise_data = cbar_kwargs.pop("_use_concise_date", False)
+
     cbar_kwargs.setdefault("extend", cmap_params["extend"])
     if cbar_ax is None:
         cbar_kwargs.setdefault("ax", ax)
@@ -723,6 +725,9 @@ def _add_colorbar(primitive, ax, cbar_ax, cbar_kwargs, cmap_params):
     fig = ax.get_figure()
     cbar = fig.colorbar(primitive, **cbar_kwargs)
 
+    if _use_concise_data:
+        _set_concise_date(ax=cbar.ax, axis="y")
+
     return cbar
 
 

xarray/tests/test_plot.py

@@ -3407,3 +3407,22 @@ def test_plot1d_filtered_nulls() -> None:
         actual = pc.get_offsets().shape[0]
 
         assert expected == actual
+
+
+@requires_matplotlib
+@pytest.mark.filterwarnings("ignore:Converting non-nanosecond")
+@pytest.mark.parametrize("plotfunc", ["lines", "scatter"])
+def test_plot1d_datetime_hue(plotfunc: str) -> None:
+    time = np.arange(
+        np.datetime64("2020-01-01"),
+        np.datetime64("2021-01-01"),
+        np.timedelta64(1, "D"),
+    )
+    data = np.arange(time.size)
+    darray = xr.DataArray(data=data, dims=("time",), coords={"time": time})
+
+    primitive = getattr(darray.plot, plotfunc)(x="time", hue="time")
+
+    # colorbar should view datetime as numerical and use readable concise dates:
+    number_of_ticks = len(primitive.colorbar.ax.get_ymajorticklabels())
+    assert number_of_ticks < 30