BUG: preserve index name when grouping by level

Author: wesm

pandas/core/frame.py

@@ -23,7 +23,7 @@
 
 from pandas.core.common import (isnull, notnull, PandasError, adjoin,
                                 _try_sort, _pfixed, _default_index,
-                                _infer_dtype, _stringify, _maybe_upcast)
+                                _stringify, _maybe_upcast)
 from pandas.core.daterange import DateRange
 from pandas.core.generic import NDFrame
 from pandas.core.index import Index, MultiIndex, NULL_INDEX, _ensure_index

pandas/core/groupby.py

@@ -5,7 +5,7 @@
 
 from pandas.core.frame import DataFrame
 from pandas.core.generic import NDFrame, PandasObject
-from pandas.core.index import Index, Int64Index, MultiIndex
+from pandas.core.index import Index, MultiIndex
 from pandas.core.internals import BlockManager
 from pandas.core.reshape import get_group_index
 from pandas.core.series import Series
@@ -536,6 +536,8 @@ def __init__(self, index, grouper=None, name=None, level=None):
 
             inds = index.labels[level]
             labels = index.levels[level].take(inds)
+            if self.name is None:
+                self.name = index.names[level]
 
             if grouper is not None:
                 self.grouper = labels.map(self.grouper)
@@ -619,7 +621,7 @@ def _get_groupings(obj, grouper=None, axis=0, level=None):
             ping = Grouping(group_axis, arg, name=name, level=level)
             groupings.append(ping)
     else:
-        name = 'key'
+        name = None
         if isinstance(grouper, basestring):
             exclusions.append(grouper)
             name = grouper

pandas/tests/test_frame.py

@@ -1210,6 +1210,9 @@ def test_from_records_tuples(self):
         assert_frame_equal(result, df)
         assert_frame_equal(result2, df)
 
+        result = DataFrame.from_records(tuples)
+        self.assert_(np.array_equal(result.columns, range(4)))
+
     def test_get_agg_axis(self):
         cols = self.frame._get_agg_axis(0)
         self.assert_(cols is self.frame.columns)

pandas/tests/test_groupby.py

@@ -730,6 +730,8 @@ def test_groupby_level(self):
 
         assert_frame_equal(result0, expected0)
         assert_frame_equal(result1, expected1)
+        self.assertEquals(result0.index.name, frame.index.names[0])
+        self.assertEquals(result1.index.name, frame.index.names[1])
 
         # groupby level name
         result0 = frame.groupby(level='first').sum()

pandas/tests/test_multilevel.py

@@ -293,6 +293,7 @@ def _check_counts(frame, axis=0):
             for i in range(index.nlevels):
                 result = frame.count(axis=axis, level=i)
                 expected = frame.groupby(axis=axis, level=i).count(axis=axis)
+                assert_frame_equal(result, expected.reindex_like(result))
 
         self.frame.ix[1, [1, 2]] = np.nan
         self.frame.ix[7, [0, 1]] = np.nan
@@ -308,6 +309,10 @@ def _check_counts(frame, axis=0):
         df = tm.makeTimeDataFrame()
         self.assertRaises(Exception, df.count, level=0)
 
+        self.frame['D'] = 'foo'
+        result = self.frame.count(level=0, numeric_only=True)
+        assert_almost_equal(result.columns, ['A', 'B', 'C'])
+
     def test_count_level_series(self):
         index = MultiIndex(levels=[['foo', 'bar', 'baz'],
                                    ['one', 'two', 'three', 'four']],