BUG: Non-string loffset not applied when resampling a timeseries

closes #13218 closes #15002 closes #14213

Author: wcwagner

doc/source/whatsnew/v0.20.0.txt

@@ -328,6 +328,7 @@ Bug Fixes
 
 
 
+- Bug in ``resample``, where a non-string ```loffset`` argument would not be applied when resampling a timeseries (:issue:`13218`)
 
 
 
@@ -337,4 +338,15 @@ Bug Fixes
 - Require at least 0.23 version of cython to avoid problems with character encodings (:issue:`14699`)
 - Bug in converting object elements of array-like objects to unsigned 64-bit integers (:issue:`4471`, :issue:`14982`)
 - Bug in ``pd.pivot_table()`` where no error was raised when values argument was not in the columns (:issue:`14938`)
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 - Bug in ``pd.read_csv()`` for the C engine where ``usecols`` were being indexed incorrectly with ``parse_dates`` (:issue:`14792`)

pandas/tseries/resample.py

@@ -323,6 +323,11 @@ def aggregate(self, arg, *args, **kwargs):
  *args,
  **kwargs)
 
+ # if arg was a string, _aggregate called resampler's _downsample or
+ # _groupby_and_agg methods, which would've already applied the loffset
+ if not isinstance(arg, compat.string_types):
+ result = self._apply_loffset(result)
+
  return result
 
  agg = aggregate
@@ -381,7 +386,7 @@ def _gotitem(self, key, ndim, subset=None):
  return grouped
 
  def _groupby_and_aggregate(self, how, grouper=None, *args, **kwargs):
- """ revaluate the obj with a groupby aggregation """
+ """ re-evaluate the obj with a groupby aggregation """
 
  if grouper is None:
  self._set_binner()
@@ -409,7 +414,14 @@ def _groupby_and_aggregate(self, how, grouper=None, *args, **kwargs):
  return self._wrap_result(result)
 
  def _apply_loffset(self, result):
- """if loffset if set, offset the result index"""
+ """
+ if loffset is set, offset the result index
+
+ Parameters
+ ----------
+ result : Series or DataFrame
+ the result of resample
+ """
  loffset = self.loffset
  if isinstance(loffset, compat.string_types):
  loffset = to_offset(self.loffset)
@@ -419,6 +431,7 @@ def _apply_loffset(self, result):
  isinstance(result.index, DatetimeIndex) and
  len(result.index) > 0
  )
+
  if needs_offset:
  result.index = result.index + loffset
 
@@ -797,6 +810,11 @@ def aggregate(self, arg, *args, **kwargs):
  if result is None:
  result = self._downsample(arg, *args, **kwargs)
 
+ # if arg was a string, _aggregate called resamplers' _downsample or
+ # _groupby_and_agg methods, which would've already applied the loffset
+ if not isinstance(arg, compat.string_types):
+ result = self._apply_loffset(result)
+
  return result
 
  agg = aggregate

pandas/tseries/tests/test_resample.py

@@ -24,7 +24,7 @@
 from pandas.tseries.period import period_range, PeriodIndex, Period
 from pandas.tseries.resample import (DatetimeIndex, TimeGrouper,
  DatetimeIndexResampler)
-from pandas.tseries.tdi import timedelta_range
+from pandas.tseries.tdi import timedelta_range, TimedeltaIndex
 from pandas.util.testing import (assert_series_equal, assert_almost_equal,
  assert_frame_equal, assert_index_equal)
 from pandas._period import IncompatibleFrequency
@@ -769,6 +769,36 @@ def test_resample_empty_dtypes(self):
  # (ex: doing mean with dtype of np.object)
  pass
 
+ def test_resample_loffset_arg_type(self):
+ # GH 13218, 15002
+ df = self.create_series().to_frame('value')
+ expected_means = [df.values[i:i + 2].mean()
+ for i in range(0, len(df.values), 2)]
+ expected_index = self.create_index(df.index[0],
+ periods=len(df.index) / 2,
+ freq='2D')
+ # loffset coreces PeriodIndex to DateTimeIndex
+ if isinstance(expected_index, PeriodIndex):
+ expected_index = expected_index.to_timestamp()
+ expected_index += timedelta(hours=2)
+ expected = DataFrame({'value': expected_means}, index=expected_index)
+ for arg in ['mean', {'value': 'mean'}, ['mean']]:
+ result_agg = df.resample('2D', loffset='2H').agg(arg)
+ with tm.assert_produces_warning(FutureWarning,
+ check_stacklevel=False):
+ result_how = df.resample('2D', how=arg, loffset='2H')
+ if isinstance(arg, list):
+ expected.columns = pd.MultiIndex.from_tuples([('value',
+ 'mean')])
+ # GH 13022, 7687 - TODO: fix resample w/ TimedeltaIndex
+ if isinstance(expected.index, TimedeltaIndex):
+ with tm.assertRaises(AssertionError):
+ assert_frame_equal(result_agg, expected)
+ assert_frame_equal(result_how, expected)
+ else:
+ assert_frame_equal(result_agg, expected)
+ assert_frame_equal(result_how, expected)
+
 
 class TestDatetimeIndex(Base, tm.TestCase):
  _multiprocess_can_split_ = True