Merge pull request #5826 from danielballan/extract-docstring

DOC: Add example to extract docstring, and re-explain change to match.

Author: jreback

doc/source/basics.rst

@@ -1029,7 +1029,7 @@ with more than one group returns a DataFrame with one column per group.
 
    Series(['a1', 'b2', 'c3']).str.extract('([ab])(\d)')
 
-Elements that do not match return a row of ``NaN``s.
+Elements that do not match return a row filled with ``NaN``.
 Thus, a Series of messy strings can be "converted" into a
 like-indexed Series or DataFrame of cleaned-up or more useful strings,
 without necessitating ``get()`` to access tuples or ``re.match`` objects.
@@ -1051,18 +1051,35 @@ can also be used.
 Testing for Strings that Match or Contain a Pattern
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
-In previous versions, *extracting* match groups was accomplished by ``match``,
-which returned a not-so-convenient Series of tuples. Starting in version 0.14,
-the default behavior of match will change. It will return a boolean
-indexer, analagous to the method ``contains``.
 
-The distinction between
-``match`` and ``contains`` is strictness: ``match`` relies on
-strict ``re.match`` while ``contains`` relies on ``re.search``.
+You can check whether elements contain a pattern:
 
-In version 0.13, ``match`` performs its old, deprecated behavior by default,
-but the new behavior is availabe through the keyword argument
-``as_indexer=True``.
+.. ipython:: python
+
+   pattern = r'[a-z][0-9]'
+   Series(['1', '2', '3a', '3b', '03c']).contains(pattern)
+
+or match a pattern:
+
+
+.. ipython:: python
+
+   Series(['1', '2', '3a', '3b', '03c']).match(pattern, as_indexer=True)
+
+The distinction between ``match`` and ``contains`` is strictness: ``match`` 
+relies on strict ``re.match``, while ``contains`` relies on ``re.search``.
+
+.. warning::
+
+   In previous versions, ``match`` was for *extracting* groups,
+   returning a not-so-convenient Series of tuples. The new method ``extract``
+   (described in the previous section) is now preferred.
+
+   This old, deprecated behavior of ``match`` is still the default. As
+   demonstrated above, use the new behavior by setting ``as_indexer=True``.
+   In this mode, ``match`` is analagous to ``contains``, returning a boolean
+   Series. The new behavior will become the default behavior in a future 
+   release.
 
 Methods like ``match``, ``contains``, ``startswith``, and ``endswith`` take
  an extra ``na`` arguement so missing values can be considered True or False:

pandas/core/strings.py

@@ -164,6 +164,11 @@ def str_contains(arr, pat, case=True, flags=0, na=np.nan):
 
     Returns
     -------
+    Series of boolean values
+        
+    See Also
+    --------
+    match : analagous, but stricter, relying on re.match instead of re.search
 
     """
     if not case:
@@ -326,11 +331,22 @@ def str_match(arr, pat, case=True, flags=0, na=np.nan, as_indexer=False):
     as_indexer : False, by default, gives deprecated behavior better achieved
         using str_extract. True return boolean indexer.
 
+    Returns
+    -------
+    boolean Series 
+        if as_indexer=True
+    Series of tuples
+        if as_indexer=False, default but deprecated
 
     Returns
     -------
-    matches : boolean array (if as_indexer=True)
-    matches : array of tuples (if as_indexer=False, default but deprecated)
+    Series of boolean values
+        
+    See Also
+    --------
+    contains : analagous, but less strict, relying on re.search instead of 
+        re.match
+    extract : now preferred to the deprecated usage of match (as_indexer=False)
 
     Notes
     -----
@@ -385,10 +401,27 @@ def str_extract(arr, pat, flags=0):
     -------
     extracted groups : Series (one group) or DataFrame (multiple groups)
 
+    Examples
+    --------
+    A pattern with one group will return a Series. Non-matches will be NaN.
 
-    Notes
-    -----
-    Compare to the string method match, which returns re.match objects.
+    >>> Series(['a1', 'b2', 'c3']).str.extract('[ab](\d)')
+    0      1
+    1      2
+    2    NaN
+    dtype: object
+
+    A pattern with more than one group will return a DataFrame.
+    
+    >>> Series(['a1', 'b2', 'c3']).str.extract('([ab])(\d)')
+
+    A pattern may contain optional groups.
+    
+    >>> Series(['a1', 'b2', 'c3']).str.extract('([ab])?(\d)')
+
+    Named groups will become column names in the result.
+    
+    >>> Series(['a1', 'b2', 'c3']).str.extract('(?P<letter>[ab])(?P<digit>\d)')
     """
     regex = re.compile(pat, flags=flags)