BUG: close #871, concat on axis=1 and ignore_index=True fixed

pandas/tools/merge.py

@@ -761,13 +761,17 @@ def get_result(self):
             new_data = self._get_concatenated_data()
             return self.objs[0]._from_axes(new_data, self.new_axes)
 
+    def _get_fresh_axis(self):
+        return Index(np.arange(len(self._get_concat_axis())))
+
     def _get_concatenated_data(self):
         try:
             # need to conform to same other (joined) axes for block join
             reindexed_data = self._get_reindexed_data()
 
             blockmaps = []
             for data in reindexed_data:
+                data = data.consolidate()
                 type_map = dict((type(blk), blk) for blk in data.blocks)
                 blockmaps.append(type_map)
             kinds = _get_all_block_kinds(blockmaps)
@@ -777,6 +781,10 @@ def _get_concatenated_data(self):
                 klass_blocks = [mapping.get(kind) for mapping in blockmaps]
                 stacked_block = self._concat_blocks(klass_blocks)
                 new_blocks.append(stacked_block)
+
+            if self.axis == 0 and self.ignore_index:
+                self.new_axes[0] = self._get_fresh_axis()
+
             new_data = BlockManager(new_blocks, self.new_axes)
         except Exception:  # EAFP
             # should not be possible to fail here for the expected reason with
@@ -820,16 +828,19 @@ def _concat_blocks(self, blocks):
                                 'DataFrames')
             return make_block(concat_values, blocks[0].items, self.new_axes[0])
         else:
-            all_items = [b.items for b in blocks if b is not None]
-            if self.axis == 0 and self.keys is not None:
-                offsets = np.r_[0, np.cumsum([len(x._data.axes[self.axis]) for
-                                              x in self.objs])]
-                indexer = np.concatenate([offsets[i] + b.ref_locs
-                                          for i, b in enumerate(blocks)
-                                          if b is not None])
-                concat_items = self.new_axes[0].take(indexer)
+            offsets = np.r_[0, np.cumsum([len(x._data.axes[0]) for
+                                            x in self.objs])]
+            indexer = np.concatenate([offsets[i] + b.ref_locs
+                                        for i, b in enumerate(blocks)
+                                        if b is not None])
+            if self.ignore_index:
+                concat_items = indexer
             else:
-                concat_items = _concat_indexes(all_items)
+                concat_items = self.new_axes[0].take(indexer)
+
+            if self.ignore_index:
+                ref_items = self._get_fresh_axis()
+                return make_block(concat_values, concat_items, ref_items)
 
             return make_block(concat_values, concat_items, self.new_axes[0])
 

pandas/tools/tests/test_merge.py

@@ -963,6 +963,25 @@ def test_concat_dict(self):
         expected = concat([frames[k] for k in keys], keys=keys)
         tm.assert_frame_equal(result, expected)
 
+    def test_concat_ignore_index(self):
+        frame1 = DataFrame({"test1": ["a", "b", "c"], 
+                            "test2": [1,2,3], 
+                            "test3": [4.5, 3.2, 1.2]})
+        frame2 = DataFrame({"test3": [5.2, 2.2, 4.3]})
+        frame1.index = Index(["x", "y", "z"])
+        frame2.index = Index(["x", "y", "q"])
+
+        v1 = concat([frame1, frame2], axis=1, ignore_index=True)
+
+        nan = np.nan
+        expected = DataFrame([[nan,nan,nan, 4.3], 
+                              ['a', 1, 4.5, 5.2],
+                              ['b', 2, 3.2, 2.2],
+                              ['c', 3, 1.2, nan]], 
+                             index=Index(["q", "x", "y", "z"]))
+
+        tm.assert_frame_equal(v1, expected)
+
     def test_concat_multiindex_with_keys(self):
         index = MultiIndex(levels=[['foo', 'bar', 'baz', 'qux'],
                                    ['one', 'two', 'three']],