Merge pull request pandas-dev#6413 from jreback/32_bit_tests

TST: GH6410 / numpy 4328

Author: jreback

pandas/core/groupby.py

@@ -1849,7 +1849,6 @@ def transform(self, func, *args, **kwargs):
 
         for name, group in self:
 
-            group = com.ensure_float(group)
             object.__setattr__(group, 'name', name)
             res = wrapper(group)
             if hasattr(res, 'values'):

pandas/tests/test_groupby.py

@@ -2731,6 +2731,15 @@ def test_groupby_max_datetime64(self):
         result = df.groupby('A')['A'].max()
         assert_series_equal(result,expected)
 
+    def test_groupby_datetime64_32_bit(self):
+        # GH 6410 / numpy 4328
+        # 32-bit under 1.9-dev indexing issue
+
+        df = DataFrame({"A": range(2), "B": [pd.Timestamp('2000-01-1')]*2})
+        result = df.groupby("A")["B"].transform(min)
+        expected = Series([pd.Timestamp('2000-01-1')]*2)
+        assert_series_equal(result,expected)
+
     def test_groupby_categorical_unequal_len(self):
         import pandas as pd
         #GH3011