BUG/ENH - base argument no longer ignored in period resample

doc/source/whatsnew/v0.24.0.rst

@@ -280,6 +280,7 @@ Other Enhancements
 - :meth:`round`, :meth:`ceil`, and meth:`floor` for :class:`DatetimeIndex` and :class:`Timestamp` now support a ``nonexistent`` argument for handling datetimes that are rounded to nonexistent times. See :ref:`timeseries.timezone_nonexistent` (:issue:`22647`)
 - :class:`Resampler` now is iterable like :class:`GroupBy` (:issue:`15314`).
 - :meth:`Series.resample` and :meth:`DataFrame.resample` have gained the :meth:`Resampler.quantile` (:issue:`15023`).
+- :meth:`TimeGrouper._get_period_bins` now accounts for the base argument passed through the :class:`PeriodIndexResampler` (:issue:`23882`)
 - :meth:`pandas.core.dtypes.is_list_like` has gained a keyword ``allow_sets`` which is ``True`` by default; if ``False``,
   all instances of ``set`` will not be considered "list-like" anymore (:issue:`23061`)
 - :meth:`Index.to_frame` now supports overriding column name(s) (:issue:`22580`).

pandas/core/resample.py

@@ -1519,9 +1519,24 @@ def _get_period_bins(self, ax):
 
         start = ax.min().asfreq(self.freq, how=self.convention)
         end = ax.max().asfreq(self.freq, how='end')
+        if self.base:
+            start = start.to_timestamp()
+            end = end.to_timestamp()
+
+            p_start, p_end = _get_range_edges(start,
+                                              end,
+                                              self.freq,
+                                              closed=self.closed,
+                                              base=self.base)
+            i = None if self.freq.onOffset(start) else 1
+            j = -1 if self.freq.onOffset(end) else None
+        else:
+            p_start, p_end = start, end
+            i = j = None
 
-        labels = binner = PeriodIndex(start=start, end=end,
-                                      freq=self.freq, name=ax.name)
+        labels = binner = PeriodIndex(start=p_start, end=p_end,
+                                      freq=self.freq,
+                                      name=ax.name)[slice(i, j)]
 
         i8 = memb.asi8
         freq_mult = self.freq.n
@@ -1531,6 +1546,7 @@ def _get_period_bins(self, ax):
         i8_extend = expected_bins_count - (i8[-1] - i8[0])
         rng = np.arange(i8[0], i8[-1] + i8_extend, freq_mult)
         rng += freq_mult
+        rng -= ((freq_mult - self.base) % freq_mult)
         bins = memb.searchsorted(rng, side='left')
 
         if nat_count > 0:

pandas/tests/resample/test_period_index.py

@@ -740,3 +740,23 @@ def test_resample_with_only_nat(self):
         expected = DataFrame([], index=expected_index)
         result = frame.resample('1s').mean()
         assert_frame_equal(result, expected)
+
+    @pytest.mark.parametrize('start,end,start_freq,end_freq,base', [
+        ('19910905', '19910909 03:00', 'H', '24H', 10),
+        ('19910905', '19910909 12:00', 'H', '24H', 10),
+        ('19910905 12:00', '19910909 03:00', 'H', '24H', 10),
+        ('19910905 12:00', '19910909 12:00', 'H', '24H', 10),
+        ('19910905', '19910913 06:00', '2H', '24H', 10),
+        ('19910905', '19910905 01:39', 'Min', '5Min', 3),
+        ('19910905', '19910905 03:18', '2Min', '5Min', 3),
+    ])
+    def test_resample_with_non_zero_base(self, start, end, start_freq,
+                                         end_freq, base):
+        # GH 23882
+        s = pd.Series(range(100), index=pd.period_range('19910905',
+                                                        periods=100,
+                                                        freq=start_freq))
+        pr = (s.resample(end_freq, base=base).mean().to_timestamp()
+              .asfreq(end_freq))  # to_timestamp casts 24H -> D
+        tr = s.to_timestamp().resample(end_freq, base=base).mean()
+        assert_series_equal(pr, tr)