BUG: inserting dups into blocks ok

CLN: finished duplicate item insert/delete - whoosh! (GH3679)

BUG: insert almost working

BUG: fixed insertion of dup columns!

ENH: added allow_duplicates kw to DataFrame.insert to indicate that inserting of

     a duplicate column should be allowed (default is False)

Author: jreback

RELEASE.rst

@@ -102,6 +102,8 @@ pandas 0.11.1
     GH3675_, GH3676_).
   - Deprecated display.height, display.width is now only a formatting option
     does not control triggering of summary, similar to < 0.11.0.
+  - Add the keyword ``allow_duplicates`` to ``DataFrame.insert`` to allow a duplicate column
+    to be inserted if ``True``, default is ``False`` (same as prior to 0.11.1) (GH3679_)
 
 **Bug Fixes**
 
@@ -133,6 +135,7 @@ pandas 0.11.1
     - Duplicate indexes with and empty DataFrame.from_records will return a correct frame (GH3562_)
     - Concat to produce a non-unique columns when duplicates are across dtypes is fixed (GH3602_)
     - Non-unique indexing with a slice via ``loc`` and friends fixed (GH3659_)
+    - Allow insert/delete to non-unique columns (GH3679_)
   - Fixed bug in groupby with empty series referencing a variable before assignment. (GH3510_)
   - Fixed bug in mixed-frame assignment with aligned series (GH3492_)
   - Fixed bug in selecting month/quarter/year from a series would not select the time element
@@ -242,6 +245,8 @@ pandas 0.11.1
 .. _GH3606: https://github.com/pydata/pandas/issues/3606
 .. _GH3659: https://github.com/pydata/pandas/issues/3659
 .. _GH3649: https://github.com/pydata/pandas/issues/3649
+.. _GH3679: https://github.com/pydata/pandas/issues/3679
+.. _Gh3616: https://github.com/pydata/pandas/issues/3616
 .. _GH1818: https://github.com/pydata/pandas/issues/1818
 .. _GH3572: https://github.com/pydata/pandas/issues/3572
 .. _GH3582: https://github.com/pydata/pandas/issues/3582

doc/source/v0.11.1.txt

@@ -71,6 +71,8 @@ API changes
     ``DataFrame.fillna()`` and ``DataFrame.replace()`` instead. (GH3582_,
     GH3675_, GH3676_)
 
+  - Add the keyword ``allow_duplicates`` to ``DataFrame.insert`` to allow a duplicate column
+    to be inserted if ``True``, default is ``False`` (same as prior to 0.11.1) (GH3679_)
 
 Enhancements
 ~~~~~~~~~~~~
@@ -209,6 +211,7 @@ Bug Fixes
       and handle missing elements like unique indices (GH3561_)
     - Duplicate indexes with and empty DataFrame.from_records will return a correct frame (GH3562_)
     - Concat to produce a non-unique columns when duplicates are across dtypes is fixed (GH3602_)
+    - Allow insert/delete to non-unique columns (GH3679_)
 
     For example you can do
 
@@ -270,3 +273,4 @@ on GitHub for a complete list.
 .. _GH3676: https://github.com/pydata/pandas/issues/3676
 .. _GH3675: https://github.com/pydata/pandas/issues/3675
 .. _GH3682: https://github.com/pydata/pandas/issues/3682
+.. _GH3679: https://github.com/pydata/pandas/issues/3679

pandas/core/frame.py

@@ -2162,10 +2162,10 @@ def _set_item(self, key, value):
         value = self._sanitize_column(key, value)
         NDFrame._set_item(self, key, value)
 
-    def insert(self, loc, column, value):
+    def insert(self, loc, column, value, allow_duplicates=False):
         """
-        Insert column into DataFrame at specified location. Raises Exception if
-        column is already contained in the DataFrame
+        Insert column into DataFrame at specified location.
+        if allow_duplicates is False, Raises Exception if column is already contained in the DataFrame
 
         Parameters
         ----------
@@ -2175,7 +2175,7 @@ def insert(self, loc, column, value):
         value : int, Series, or array-like
         """
         value = self._sanitize_column(column, value)
-        self._data.insert(loc, column, value)
+        self._data.insert(loc, column, value, allow_duplicates=allow_duplicates)
 
     def _sanitize_column(self, key, value):
         # Need to make sure new columns (which go into the BlockManager as new