Normalized index type and name of empty series

Author: discort

doc/source/whatsnew/v0.21.0.txt

@@ -298,6 +298,7 @@ Groupby/Resample/Rolling
 - Bug in :func:`infer_freq` causing indices with 2-day gaps during the working week to be wrongly inferred as business daily (:issue:`16624`)
 - Bug in ``.rolling(...).quantile()`` which incorrectly used different defaults than :func:`Series.quantile()` and :func:`DataFrame.quantile()` (:issue:`9413`, :issue:`16211`)
 - Bug in ``groupby.transform()`` that would coerce boolean dtypes back to float (:issue:`16875`)
+- Bug in ``Series.resample(...).apply()`` where an empty ``Series`` modified the source index and did not return the name of a ``Series`` (:issue:`14313`)
 
 Sparse
 ^^^^^^

pandas/core/resample.py

@@ -778,6 +778,11 @@ def _wrap_result(self, result):
         # convert if needed
         if self.kind == 'period' and not isinstance(result.index, PeriodIndex):
             result.index = result.index.to_period(self.freq)
+
+        if isinstance(result, com.ABCSeries) and result.empty:
+            obj = self.obj
+            result.index = obj.index._shallow_copy(freq=to_offset(self.freq))
+            result.name = getattr(obj, 'name', None)
         return result
 
 

pandas/tests/test_resample.py

@@ -2192,6 +2192,17 @@ def test_resample_datetime_values(self):
         res = df['timestamp'].resample('2D').first()
         tm.assert_series_equal(res, exp)
 
+    def test_apply_to_empty_series(self):
+        # GH 14313
+        series = self.create_series()[:0]
+
+        for freq in ['M', 'D', 'H']:
+            result = series.resample(freq).apply(lambda x: 1)
+            expected = series.resample(freq).apply(np.sum)
+
+            assert result.name == expected.name
+            assert_series_equal(result, expected, check_dtype=False)
+
 
 class TestPeriodIndex(Base):
     _index_factory = lambda x: period_range