我有一个非常相似的pandas数据帧：
在：
import pandas as pd
df = pd.DataFrame({'blobs':['6-Feb- 1 4 Startup ZestFinance says it has built a machine-learning system that’s smart enough to find new borrowers and keep bias out of its credit analysis. 17-Feb-2014',
'Credit ratings have long been the key measure of how likely a U.S. 29—Oct-2012 consumer is to repay any loan, from mortgages to 18-0ct-12 credit cards. But the factors that FICO and other companies that create credit scores rely on—things like credit history and credit card balances—often depend on having credit already. ',
'November 22, 2012 In recent years, a crop of startup companies have launched on the premise 6—Feb- ] 4 that borrowers without such histories might still be quite likely to repay, and that their likelihood of doing so could be determined by analyzing large amounts of data, especially data that has traditionally not been part of the credit evaluation. These companies use algorithms and machine learning to find meaningful patterns in the data, alternative signs that a borrower is a good or bad credit risk.',
'March 1“, 2012 Los Angeles-based ZestFinance, founded by former Google CIO Douglas Merrill, claims to have solved this problem with a new credit-scoring platform, called ZAML. 06—Fcb—2012 The company sells the machine-learning software to lenders and also offers consulting 19—Jan— ] 2 services. Zest does not lend money itself. January 2, 1990']})
每行都有不同格式的嘈杂日期。因此，我的目标是将日期提取到另一列，例如，从上面的daata框架我想提取这样的日期：
（*） 出：
dates1 dates2
0 6-Feb-14, 17-Feb-2014 NaN
1 29—Oct-2012, 18-0ct-12 NaN
2 6—Feb- ]4 November 22, 2012
3 06—Fcb—2012, 19—Jan— ] 2 March 1“, 2012 | January 2, 1990
到目前为止，我尝试定义以下正则表达式并使用extract()从列中提取：
在：
df['col1'] = df['blobs'].str.extract(r"^(?:(?:31(\/|-|\.)(?:0?[13578]|1[02]|(?:Jan|Mar|May|Jul|Aug|Oct|Dec)))\1|(?:(?:29|30)(\/|-|\.)(?:0?[1,3-9]|1[0-2]|(?:Jan|Mar|Apr|May|Jun|Jul|Aug|Sep|Oct|Nov|Dec))\2))(?:(?:1[6-9]|[2-9]\d)?\d{2})$|^(?:29(\/|-|\.)(?:0?2|(?:Feb))\3(?:(?:(?:1[6-9]|[2-9]\d)?(?:0[48]|[2468][048]|[13579][26])|(?:(?:16|[2468][048]|[3579][26])00))))$|^(?:0?[1-9]|1\d|2[0-8])(\/|-|\.)(?:(?:0?[1-9]|(?:Jan|Feb|Mar|Apr|May|Jun|Jul|Aug|Sep))|(?:1[0-2]|(?:Oct|Nov|Dec)))\4(?:(?:1[6-9]|[2-9]\d)?\d{2})$")
df
但是我收到以下错误，我希望有一个更健壮的方法。因此，这是获得（*）
的最佳方式输出：
KeyError Traceback (most recent call last)
/usr/local/lib/python3.5/site-packages/pandas/indexes/base.py in get_loc(self, key, method, tolerance)
2133 try:
-> 2134 return self._engine.get_loc(key)
2135 except KeyError:
pandas/index.pyx in pandas.index.IndexEngine.get_loc (pandas/index.c:4433)()
pandas/index.pyx in pandas.index.IndexEngine.get_loc (pandas/index.c:4279)()
pandas/src/hashtable_class_helper.pxi in pandas.hashtable.PyObjectHashTable.get_item (pandas/hashtable.c:13742)()
pandas/src/hashtable_class_helper.pxi in pandas.hashtable.PyObjectHashTable.get_item (pandas/hashtable.c:13696)()
KeyError: 'date_format_3'
During handling of the above exception, another exception occurred:
KeyError Traceback (most recent call last)
/usr/local/lib/python3.5/site-packages/pandas/core/internals.py in set(self, item, value, check)
3667 try:
-> 3668 loc = self.items.get_loc(item)
3669 except KeyError:
/usr/local/lib/python3.5/site-packages/pandas/indexes/base.py in get_loc(self, key, method, tolerance)
2135 except KeyError:
-> 2136 return self._engine.get_loc(self._maybe_cast_indexer(key))
2137
pandas/index.pyx in pandas.index.IndexEngine.get_loc (pandas/index.c:4433)()
pandas/index.pyx in pandas.index.IndexEngine.get_loc (pandas/index.c:4279)()
pandas/src/hashtable_class_helper.pxi in pandas.hashtable.PyObjectHashTable.get_item (pandas/hashtable.c:13742)()
pandas/src/hashtable_class_helper.pxi in pandas.hashtable.PyObjectHashTable.get_item (pandas/hashtable.c:13696)()
KeyError: 'date_format_3'
During handling of the above exception, another exception occurred:
ValueError Traceback (most recent call last)
<ipython-input-3-ec929aa5341c> in <module>()
----> 1 df['date_format_3'] = df['text'].str.extract(r"^(?:(?:31(\/|-|\.)(?:0?[13578]|1[02]|(?:Jan|Mar|May|Jul|Aug|Oct|Dec)))\1|(?:(?:29|30)(\/|-|\.)(?:0?[1,3-9]|1[0-2]|(?:Jan|Mar|Apr|May|Jun|Jul|Aug|Sep|Oct|Nov|Dec))\2))(?:(?:1[6-9]|[2-9]\d)?\d{2})$|^(?:29(\/|-|\.)(?:0?2|(?:Feb))\3(?:(?:(?:1[6-9]|[2-9]\d)?(?:0[48]|[2468][048]|[13579][26])|(?:(?:16|[2468][048]|[3579][26])00))))$|^(?:0?[1-9]|1\d|2[0-8])(\/|-|\.)(?:(?:0?[1-9]|(?:Jan|Feb|Mar|Apr|May|Jun|Jul|Aug|Sep))|(?:1[0-2]|(?:Oct|Nov|Dec)))\4(?:(?:1[6-9]|[2-9]\d)?\d{2})$", expand = True)
2 df
/usr/local/lib/python3.5/site-packages/pandas/core/frame.py in __setitem__(self, key, value)
2417 else:
2418 # set column
-> 2419 self._set_item(key, value)
2420
2421 def _setitem_slice(self, key, value):
/usr/local/lib/python3.5/site-packages/pandas/core/frame.py in _set_item(self, key, value)
2484 self._ensure_valid_index(value)
2485 value = self._sanitize_column(key, value)
-> 2486 NDFrame._set_item(self, key, value)
2487
2488 # check if we are modifying a copy
/usr/local/lib/python3.5/site-packages/pandas/core/generic.py in _set_item(self, key, value)
1498
1499 def _set_item(self, key, value):
-> 1500 self._data.set(key, value)
1501 self._clear_item_cache()
1502
/usr/local/lib/python3.5/site-packages/pandas/core/internals.py in set(self, item, value, check)
3669 except KeyError:
3670 # This item wasn't present, just insert at end
-> 3671 self.insert(len(self.items), item, value)
3672 return
3673
/usr/local/lib/python3.5/site-packages/pandas/core/internals.py in insert(self, loc, item, value, allow_duplicates)
3770
3771 block = make_block(values=value, ndim=self.ndim,
-> 3772 placement=slice(loc, loc + 1))
3773
3774 for blkno, count in _fast_count_smallints(self._blknos[loc:]):
/usr/local/lib/python3.5/site-packages/pandas/core/internals.py in make_block(values, placement, klass, ndim, dtype, fastpath)
2683 placement=placement, dtype=dtype)
2684
-> 2685 return klass(values, ndim=ndim, fastpath=fastpath, placement=placement)
2686
2687 # TODO: flexible with index=None and/or items=None
/usr/local/lib/python3.5/site-packages/pandas/core/internals.py in __init__(self, values, ndim, fastpath, placement, **kwargs)
1815
1816 super(ObjectBlock, self).__init__(values, ndim=ndim, fastpath=fastpath,
-> 1817 placement=placement, **kwargs)
1818
1819 @property
/usr/local/lib/python3.5/site-packages/pandas/core/internals.py in __init__(self, values, placement, ndim, fastpath)
107 raise ValueError('Wrong number of items passed %d, placement '
108 'implies %d' % (len(self.values),
--> 109 len(self.mgr_locs)))
110
111 @property
ValueError: Wrong number of items passed 4, placement implies 1
答案 0 :(得分：0)
您必须在str.extract()中用括号定义一个捕获组。
我扩展/纠正了正则表达式模式，但需要更多工作。 （您可以查看并试验this regular expression on regex101）
df['blobs'].str.extract("(\d{1,2}[\s-]\w+[\s-]\d{2,4}|\w+[\s-]\d{1,2}[\",\s-]+\d{2,4})", expand = True)
输出：
0
0 17-Feb-2014
1 18-0ct-12
2 November 22, 2012
3 January 2, 1990