PERF: improve .str perf for all-string values

Author: sinhrks

pandas/core/strings.py

@@ -116,12 +116,12 @@ def _length_check(others):
  return n
 
 
-def _na_map(f, arr, na_result=np.nan, dtype=object):
+def _na_map(f, arr, na_result=np.nan, dtype=object, np_f=None):
  # should really _check_ for NA
- return _map(f, arr, na_mask=True, na_value=na_result, dtype=dtype)
+ return _map(f, arr, na_mask=True, na_value=na_result, dtype=dtype, np_f=np_f)
 
 
-def _map(f, arr, na_mask=False, na_value=np.nan, dtype=object):
+def _map(f, arr, na_mask=False, na_value=np.nan, dtype=object, np_f=None):
  from pandas.core.series import Series
 
  if not len(arr):
@@ -131,6 +131,14 @@ def _map(f, arr, na_mask=False, na_value=np.nan, dtype=object):
  arr = arr.values
  if not isinstance(arr, np.ndarray):
  arr = np.asarray(arr, dtype=object)
+
+ # short path for all-string array
+ if np_f is not None and lib.is_string_array(arr):
+ try:
+ return np_f(arr.values.astype(unicode))
+ except Exception:
+ pass
+
  if na_mask:
  mask = isnull(arr)
  try:
@@ -686,14 +694,17 @@ def str_pad(arr, width, side='left', fillchar=' '):
 
  if side == 'left':
  f = lambda x: x.rjust(width, fillchar)
+ np_f = lambda x: np.core.defchararray.ljust(x, width, fillchar)
  elif side == 'right':
  f = lambda x: x.ljust(width, fillchar)
+ np_f = lambda x: np.core.defchararray.rjust(x, width, fillchar)
  elif side == 'both':
  f = lambda x: x.center(width, fillchar)
+ np_f = lambda x: np.core.defchararray.lower(x, width, fillchar)
  else: # pragma: no cover
  raise ValueError('Invalid side')
 
- return _na_map(f, arr)
+ return _na_map(f, arr, np_f=np_f)
 
 
 def str_split(arr, pat=None, n=None):
@@ -720,17 +731,21 @@ def str_split(arr, pat=None, n=None):
  if n is None or n == 0:
  n = -1
  f = lambda x: x.split(pat, n)
+ np_f = lambda x: np.core.defchararray.split(x, pat, n)
  else:
  if len(pat) == 1:
  if n is None or n == 0:
  n = -1
  f = lambda x: x.split(pat, n)
+ np_f = lambda x: np.core.defchararray.split(x, pat, n)
  else:
  if n is None or n == -1:
  n = 0
  regex = re.compile(pat)
  f = lambda x: regex.split(x, maxsplit=n)
- res = _na_map(f, arr)
+ # numpy doesn't support regex
+ np_f = None
+ res = _na_map(f, arr, np_f=np_f)
  return res
 
 
@@ -946,7 +961,8 @@ def str_decode(arr, encoding, errors="strict"):
  decoded : Series/Index of objects
  """
  f = lambda x: x.decode(encoding, errors)
- return _na_map(f, arr)
+ np_f = lambda x: np.core.defchararray.decode(x, errors)
+ return _na_map(f, arr, np_f=np_f)
 
 
 def str_encode(arr, encoding, errors="strict"):
@@ -964,12 +980,13 @@ def str_encode(arr, encoding, errors="strict"):
  encoded : Series/Index of objects
  """
  f = lambda x: x.encode(encoding, errors)
- return _na_map(f, arr)
+ np_f = lambda x: np.core.defchararray.encode(x, errors)
+ return _na_map(f, arr, np_f=np_f)
 
 
-def _noarg_wrapper(f, docstring=None, **kargs):
+def _noarg_wrapper(f, docstring=None, np_f=None, **kargs):
  def wrapper(self):
- result = _na_map(f, self.series, **kargs)
+ result = _na_map(f, self.series, np_f=np_f, **kargs)
  return self._wrap_result(result)
 
  wrapper.__name__ = f.__name__
@@ -1443,7 +1460,8 @@ def rindex(self, sub, start=0, end=None):
  _shared_docs['swapcase'] = dict(type='be swapcased', method='swapcase')
  lower = _noarg_wrapper(lambda x: x.lower(),
  docstring=_shared_docs['casemethods'] %
- _shared_docs['lower'])
+ _shared_docs['lower'],
+ np_f=np.core.defchararray.lower)
  upper = _noarg_wrapper(lambda x: x.upper(),
  docstring=_shared_docs['casemethods'] %
  _shared_docs['upper'])
@@ -1452,7 +1470,8 @@ def rindex(self, sub, start=0, end=None):
  _shared_docs['title'])
  capitalize = _noarg_wrapper(lambda x: x.capitalize(),
  docstring=_shared_docs['casemethods'] %
- _shared_docs['capitalize'])
+ _shared_docs['capitalize'],
+ np_f=np.core.defchararray.capitalize)
  swapcase = _noarg_wrapper(lambda x: x.swapcase(),
  docstring=_shared_docs['casemethods'] %
  _shared_docs['swapcase'])