BUG: Fix for #37454: allow reversed axis when plotting with TimedeltaIndex (#37469)

Author: theavey

doc/source/whatsnew/v1.2.0.rst

@@ -659,9 +659,10 @@ Plotting
 - Bug in :meth:`DataFrame.plot` was rotating xticklabels when ``subplots=True``, even if the x-axis wasn't an irregular time series (:issue:`29460`)
 - Bug in :meth:`DataFrame.plot` where a marker letter in the ``style`` keyword sometimes causes a ``ValueError`` (:issue:`21003`)
 - Twinned axes were losing their tick labels which should only happen to all but the last row or column of 'externally' shared axes (:issue:`33819`)
+- Bug in :meth:`Series.plot` and :meth:`DataFrame.plot` was throwing :exc:`ValueError` with a :class:`Series` or :class:`DataFrame`
+  indexed by a :class:`TimedeltaIndex` with a fixed frequency when x-axis lower limit was greater than upper limit (:issue:`37454`)
 - Bug in :meth:`DataFrameGroupBy.boxplot` when ``subplots=False``, a KeyError would raise (:issue:`16748`)
 
-
 Groupby/resample/rolling
 ^^^^^^^^^^^^^^^^^^^^^^^^
 

pandas/plotting/_matplotlib/converter.py

@@ -1072,7 +1072,7 @@ def format_timedelta_ticks(x, pos, n_decimals: int) -> str:
 
     def __call__(self, x, pos=0) -> str:
         (vmin, vmax) = tuple(self.axis.get_view_interval())
-        n_decimals = int(np.ceil(np.log10(100 * 1e9 / (vmax - vmin))))
+        n_decimals = int(np.ceil(np.log10(100 * 1e9 / abs(vmax - vmin))))
         if n_decimals > 9:
             n_decimals = 9
         return self.format_timedelta_ticks(x, pos, n_decimals)

pandas/tests/plotting/test_converter.py

@@ -372,3 +372,14 @@ def test_format_timedelta_ticks(self, x, decimal, format_expected):
         tdc = converter.TimeSeries_TimedeltaFormatter
         result = tdc.format_timedelta_ticks(x, pos=None, n_decimals=decimal)
         assert result == format_expected
+
+    @pytest.mark.parametrize("view_interval", [(1, 2), (2, 1)])
+    def test_call_w_different_view_intervals(self, view_interval, monkeypatch):
+        # previously broke on reversed xlmits; see GH37454
+        class mock_axis:
+            def get_view_interval(self):
+                return view_interval
+
+        tdc = converter.TimeSeries_TimedeltaFormatter()
+        monkeypatch.setattr(tdc, "axis", mock_axis())
+        tdc(0.0, 0)

pandas/tests/plotting/test_series.py

@@ -983,3 +983,16 @@ def test_xlabel_ylabel_series(self, kind, index_name, old_label, new_label):
         ax = ser.plot(kind=kind, ylabel=new_label, xlabel=new_label)
         assert ax.get_ylabel() == new_label
         assert ax.get_xlabel() == new_label
+
+    @pytest.mark.parametrize(
+        "index",
+        [
+            pd.timedelta_range(start=0, periods=2, freq="D"),
+            [pd.Timedelta(days=1), pd.Timedelta(days=2)],
+        ],
+    )
+    def test_timedelta_index(self, index):
+        # GH37454
+        xlims = (3, 1)
+        ax = Series([1, 2], index=index).plot(xlim=(xlims))
+        assert ax.get_xlim() == (3, 1)