ENH: Add prefix parameters for join method.

pandas/core/frame.py

@@ -3702,6 +3702,7 @@ def append(self, other, ignore_index=False, verify_integrity=False):
  verify_integrity=verify_integrity)
 
  def join(self, other, on=None, how='left', lsuffix='', rsuffix='',
+ lprefix='', rprefix='',
  sort=False):
  """
  Join columns with other DataFrame either on index or on a key
@@ -3746,9 +3747,11 @@ def join(self, other, on=None, how='left', lsuffix='', rsuffix='',
  """
  # For SparseDataFrame's benefit
  return self._join_compat(other, on=on, how=how, lsuffix=lsuffix,
- rsuffix=rsuffix, sort=sort)
+ rsuffix=rsuffix, lprefix=lprefix,
+ rprefix=rprefix, sort=sort)
 
  def _join_compat(self, other, on=None, how='left', lsuffix='', rsuffix='',
+ lprefix='', rprefix='',
  sort=False):
  from pandas.tools.merge import merge, concat
 
@@ -3760,7 +3763,9 @@ def _join_compat(self, other, on=None, how='left', lsuffix='', rsuffix='',
  if isinstance(other, DataFrame):
  return merge(self, other, left_on=on, how=how,
  left_index=on is None, right_index=True,
- suffixes=(lsuffix, rsuffix), sort=sort)
+ suffixes=(lsuffix, rsuffix),
+ prefixes=(lprefix, rprefix),
+ sort=sort)
  else:
  if on is not None:
  raise ValueError('Joining multiple DataFrames only supported'

pandas/core/internals.py

@@ -3898,6 +3898,31 @@ def rrenamer(x):
  _transform_index(right, rrenamer))
 
 
+def items_overlap_with_suffix_and_prefix(
+ left, lsuffix, lprefix, right, rsuffix, rprefix):
+ to_rename = left.intersection(right)
+ if len(to_rename) == 0:
+ return left, right
+ else:
+ if not lsuffix and not rsuffix and not lprefix and not rprefix:
+ raise ValueError('columns overlap but no suffix or prefix specified: %s' %
+ to_rename)
+
+ def lrenamer(x):
+ if x in to_rename:
+ return '%s%s%s' % (lprefix, x, lsuffix)
+ return x
+
+ def rrenamer(x):
+ if x in to_rename:
+ return '%s%s%s' % (rprefix, x, rsuffix)
+ return x
+
+ return (_transform_index(left, lrenamer),
+ _transform_index(right, rrenamer))
+
+
+
 def _transform_index(index, func):
  """
  Apply function to all values found in index.

pandas/sparse/frame.py

@@ -607,13 +607,13 @@ def _reindex_with_indexers(self, reindexers, method=None, fill_value=None, limit
  return SparseDataFrame(new_arrays, index=index, columns=columns).__finalize__(self)
 
  def _join_compat(self, other, on=None, how='left', lsuffix='', rsuffix='',
- sort=False):
+ lprefix='', rprefix='', sort=False):
  if on is not None:
  raise NotImplementedError("'on' keyword parameter is not yet "
  "implemented")
- return self._join_index(other, how, lsuffix, rsuffix)
+ return self._join_index(other, how, lsuffix, rsuffix, lprefix, rprefix)
 
- def _join_index(self, other, how, lsuffix, rsuffix):
+ def _join_index(self, other, how, lsuffix, rsuffix, lprefix, rprefix):
  if isinstance(other, Series):
  if other.name is None:
  raise ValueError('Other Series must have a name')
@@ -626,26 +626,26 @@ def _join_index(self, other, how, lsuffix, rsuffix):
  this = self.reindex(join_index)
  other = other.reindex(join_index)
 
- this, other = this._maybe_rename_join(other, lsuffix, rsuffix)
+ this, other = this._maybe_rename_join(other, lsuffix, rsuffix, lprefix, rprefix)
 
  from pandas import concat
  return concat([this, other], axis=1, verify_integrity=True)
 
- def _maybe_rename_join(self, other, lsuffix, rsuffix):
+ def _maybe_rename_join(self, other, lsuffix, rsuffix, lprefix, rprefix):
  to_rename = self.columns.intersection(other.columns)
  if len(to_rename) > 0:
- if not lsuffix and not rsuffix:
- raise ValueError('columns overlap but no suffix specified: %s'
+ if not lsuffix and not rsuffix and not lprefix and not rprefix:
+ raise ValueError('columns overlap but no suffix or prefix specified: %s'
  % to_rename)
 
  def lrenamer(x):
  if x in to_rename:
- return '%s%s' % (x, lsuffix)
+ return '%s%s%s' % (lprefix, x, lsuffix)
  return x
 
  def rrenamer(x):
  if x in to_rename:
- return '%s%s' % (x, rsuffix)
+ return '%s%s%s' % (rprefix, x, rsuffix)
  return x
 
  this = self.rename(columns=lrenamer)

pandas/tools/merge.py

@@ -15,6 +15,7 @@
  _ensure_index, _get_consensus_names,
  _all_indexes_same)
 from pandas.core.internals import (items_overlap_with_suffix,
+ items_overlap_with_suffix_and_prefix,
  concatenate_block_managers)
 from pandas.util.decorators import Appender, Substitution
 from pandas.core.common import ABCSeries
@@ -31,10 +32,11 @@
 @Appender(_merge_doc, indents=0)
 def merge(left, right, how='inner', on=None, left_on=None, right_on=None,
  left_index=False, right_index=False, sort=False,
- suffixes=('_x', '_y'), copy=True):
+ suffixes=('_x', '_y'), prefixes=('', ''), copy=True):
  op = _MergeOperation(left, right, how=how, on=on, left_on=left_on,
  right_on=right_on, left_index=left_index,
  right_index=right_index, sort=sort, suffixes=suffixes,
+ prefixes=prefixes,
  copy=copy)
  return op.get_result()
 if __debug__:
@@ -161,7 +163,7 @@ class _MergeOperation(object):
  def __init__(self, left, right, how='inner', on=None,
  left_on=None, right_on=None, axis=1,
  left_index=False, right_index=False, sort=True,
- suffixes=('_x', '_y'), copy=True):
+ suffixes=('_x', '_y'), prefixes=('', ''), copy=True):
  self.left = self.orig_left = left
  self.right = self.orig_right = right
  self.how = how
@@ -173,6 +175,7 @@ def __init__(self, left, right, how='inner', on=None,
 
  self.copy = copy
  self.suffixes = suffixes
+ self.prefixes = prefixes
  self.sort = sort
 
  self.left_index = left_index
@@ -188,9 +191,12 @@ def get_result(self):
 
  ldata, rdata = self.left._data, self.right._data
  lsuf, rsuf = self.suffixes
+ lpre, rpre = self.prefixes
 
- llabels, rlabels = items_overlap_with_suffix(ldata.items, lsuf,
- rdata.items, rsuf)
+ llabels, rlabels = items_overlap_with_suffix_and_prefix(
+ ldata.items, lsuf, lpre,
+ rdata.items, rsuf, rpre
+ )
 
  lindexers = {1: left_indexer} if left_indexer is not None else {}
  rindexers = {1: right_indexer} if right_indexer is not None else {}