BUG: Bug in setitem with list-of-lists and single vs mixed types (GH7551)

doc/source/v0.14.1.txt

@@ -169,7 +169,7 @@ Bug Fixes
 - Bug in ``DataFrame.where`` with a symmetric shaped frame and a passed other of a DataFrame (:issue:`7506`)
 - Bug in Panel indexing with a multi-index axis (:issue:`7516`)
 - Regression in datetimelike slice indexing with a duplicated index and non-exact end-points (:issue:`7523`)
-
+- Bug in setitem with list-of-lists and single vs mixed types (:issue:`7551`:)
 - Bug in timeops with non-aligned Series (:issue:`7500`)
 
 

pandas/core/indexing.py

@@ -419,14 +419,20 @@ def can_do_equal_len():
                         else:
                             setter(item, np.nan)
 
-                # we have an equal len ndarray to our labels
-                elif isinstance(value, np.ndarray) and value.ndim == 2:
+                # we have an equal len ndarray/convertible to our labels
+                elif np.array(value).ndim == 2:
+
+                    # note that this coerces the dtype if we are mixed
+                    # GH 7551
+                    value = np.array(value,dtype=object)
                     if len(labels) != value.shape[1]:
                         raise ValueError('Must have equal len keys and value '
                                          'when setting with an ndarray')
 
                     for i, item in enumerate(labels):
-                        setter(item, value[:, i])
+
+                        # setting with a list, recoerces
+                        setter(item, value[:, i].tolist())
 
                 # we have an equal len list/ndarray
                 elif can_do_equal_len():

pandas/tests/test_indexing.py

@@ -1272,7 +1272,6 @@ def test_iloc_setitem_series(self):
         result = df.iloc[:,2:3]
         assert_frame_equal(result, expected)
 
-    def test_iloc_setitem_series(self):
         s = Series(np.random.randn(10), index=lrange(0,20,2))
 
         s.iloc[1] = 1
@@ -1284,6 +1283,20 @@ def test_iloc_setitem_series(self):
         result = s.iloc[:4]
         assert_series_equal(result, expected)
 
+    def test_iloc_setitem_list_of_lists(self):
+
+        # GH 7551
+        # list-of-list is set incorrectly in mixed vs. single dtyped frames
+        df = DataFrame(dict(A = np.arange(5,dtype='int64'), B = np.arange(5,10,dtype='int64')))
+        df.iloc[2:4] = [[10,11],[12,13]]
+        expected = DataFrame(dict(A = [0,1,10,12,4], B = [5,6,11,13,9]))
+        assert_frame_equal(df, expected)
+
+        df = DataFrame(dict(A = list('abcde'), B = np.arange(5,10,dtype='int64')))
+        df.iloc[2:4] = [['x',11],['y',13]]
+        expected = DataFrame(dict(A = ['a','b','x','y','e'], B = [5,6,11,13,9]))
+        assert_frame_equal(df, expected)
+
     def test_iloc_getitem_multiindex(self):
         mi_labels = DataFrame(np.random.randn(4, 3), columns=[['i', 'i', 'j'],
                                                               ['A', 'A', 'B']],