嘗試從熊貓列中提取日期時的問題？

Question

我有一個非常類似的大熊貓據幀：

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']}) 

每一行都有不同的格式有些吵日期。因此，我的目標是將日期提取到另一列，例如，從上面的daata幀我想提取日期這樣：

（*） 輸出：

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 

所以到目前爲止，我試圖與extract()限定從柱以下的正則表達式和提取：

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 

但是我收到以下錯誤，我想要一個更強大的方法。因此，這是獲得（*）

出的最佳方式：

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 

Answer 1

你必須在str.extract()用括號定義捕獲組。

我擴展/糾正了正則表達式模式，但它需要更多的工作。 （您可以查看和實驗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) 

日期：

    0 
0  17-Feb-2014 
1   18-0ct-12 
2 November 22, 2012 
3 January 2, 1990