BUG: resampling with NaT in TimedeltaIndex (#13223)

pandas/tseries/resample.py

@@ -7,7 +7,8 @@
 from pandas.core.base import AbstractMethodError, GroupByMixin
 
 from pandas.core.groupby import (BinGrouper, Grouper, _GroupBy, GroupBy,
-                                 SeriesGroupBy, groupby, PanelGroupBy)
+                                 SeriesGroupBy, groupby, PanelGroupBy,
+                                 DataError)
 
 from pandas.tseries.frequencies import to_offset, is_subperiod, is_superperiod
 from pandas.tseries.index import DatetimeIndex, date_range
@@ -1219,13 +1220,18 @@ def _get_time_delta_bins(self, ax):
             raise TypeError('axis must be a TimedeltaIndex, but got '
                             'an instance of %r' % type(ax).__name__)
 
+        if len(ax) > 0 and all(ax._isnan):
+            raise DataError('all-nan groupings not valid')
+
         if not len(ax):
             binner = labels = TimedeltaIndex(
                 data=[], freq=self.freq, name=ax.name)
             return binner, [], labels
 
-        start = ax[0]
-        end = ax[-1]
+        # Addresses GH #13223
+        start = ax.min()
+        end = ax.max()
+
         labels = binner = TimedeltaIndex(start=start,
                                          end=end,
                                          freq=self.freq,
@@ -1234,6 +1240,13 @@ def _get_time_delta_bins(self, ax):
         end_stamps = labels + 1
         bins = ax.searchsorted(end_stamps, side='left')
 
+        if ax.hasnans:
+            binner = binner.insert(0, tslib.NaT)
+            labels = labels.insert(0, tslib.NaT)
+
+            n_NaT = ax._isnan.sum()
+            bins = np.insert(bins, 0, n_NaT)
+
         # Addresses GH #10530
         if self.base > 0:
             labels += type(self.freq)(self.base)

pandas/tseries/tests/test_resample.py

@@ -1025,6 +1025,20 @@ def test_resample_timedelta_idempotency(self):
         expected = series
         assert_series_equal(result, expected)
 
+    def test_resample_timedelta_missing_values(self):
+        # GH 13223
+        index = pd.to_timedelta(['0s', pd.NaT, '2s'])
+        series = pd.Series([2, 3, 5], index=index)
+        result = series.resample('1s').mean()
+        expected = pd.Series([2, np.nan, 5], index=pd.timedelta_range(
+            start='0s', end='2s', freq='1s'))
+        assert_series_equal(result, expected)
+
+        # all NaT
+        index = pd.to_timedelta([pd.NaT, pd.NaT, pd.NaT])
+        series = pd.Series([2, 3, 5], index=index)
+        self.assertRaises(DataError, series.resample('1s').mean)
+
     def test_resample_rounding(self):
         # GH 8371
         # odd results when rounding is needed