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

doc/source/whatsnew/v1.1.4.rst

@@ -41,6 +41,8 @@ Bug fixes
 - Bug in :meth:`GroupBy.fillna` that introduced a performance regression after 1.0.5 (:issue:`36757`)
 - Bug in :meth:`DataFrame.info` was raising a ``KeyError`` when the DataFrame has integer column names (:issue:`37245`)
 - Bug in :meth:`DataFrameGroupby.apply` would drop a :class:`CategoricalIndex` when grouped on (:issue:`35792`)
+- 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`)
 
 .. ---------------------------------------------------------------------------
 

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

@@ -361,3 +361,13 @@ 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(self, view_interval, monkeypatch):
+        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)