PERF: perf regressions on insertion of columns into frame (related to 4032)

PERF: vbench for inserting cols at the beginning

Author: jreback

pandas/core/internals.py

@@ -1788,6 +1788,9 @@ def insert(self, loc, item, value, allow_duplicates=False):
             # new block
             self._add_new_block(item, value, loc=loc)
 
+            if loc != len(self.items)-1 and new_items.is_unique:
+                self.set_items_clear(new_items)
+
         except:
 
             # so our insertion operation failed, so back out of the new items
@@ -1800,8 +1803,6 @@ def insert(self, loc, item, value, allow_duplicates=False):
 
         if len(self.blocks) > 100:
             self._consolidate_inplace()
-        elif new_items.is_unique:
-            self.set_items_clear(new_items)
 
         self._known_consolidated = False
 

pandas/tests/test_frame.py

@@ -10040,11 +10040,15 @@ def test_insert_column_bug_4032(self):
         df.insert(0, 'a', [1, 2])
 
         result = df.rename(columns={})
+        str(result)
+
         expected = DataFrame([[1,1.1],[2, 2.2]],columns=['a','b'])
         assert_frame_equal(result,expected)
         df.insert(0, 'c', [1.3, 2.3])
 
         result = df.rename(columns={})
+        str(result)
+
         expected = DataFrame([[1.3,1,1.1],[2.3,2, 2.2]],columns=['c','a','b'])
         assert_frame_equal(result,expected)
 

vb_suite/frame_methods.py

@@ -125,8 +125,19 @@ def f(K=500):
         df[i] = new_col
 """
 
-frame_insert_500_columns = Benchmark('f()', setup,
-                                     start_date=datetime(2011, 1, 1))
+frame_insert_500_columns_end = Benchmark('f()', setup, start_date=datetime(2011, 1, 1))
+
+setup = common_setup + """
+N = 1000
+
+def f(K=100):
+    df = DataFrame(index=range(N))
+    new_col = np.random.randn(N)
+    for i in range(K):
+        df.insert(0,i,new_col)
+"""
+
+frame_insert_100_columns_begin = Benchmark('f()', setup, start_date=datetime(2011, 1, 1))
 
 #----------------------------------------------------------------------
 # strings methods, #2602