python - 从 SQL 数据库导入表并按日期过滤行时，将 Pandas 列解析为 Datetime

Question

我有一个 DataFrame 列名为 date。我们如何将“日期”列转换/解析为 DateTime 对象？

我使用 sql.read_frame() 从 Postgresql 数据库加载了日期列。 date 列的示例是 2013-04-04。

我想要做的是选择数据框中的所有行，这些行在特定时期内具有日期列，例如在 2013-04-01 之后和 2013-04- 之前04.

我在下面的尝试给出了错误 'Series' object has no attribute 'read'

尝试

import dateutil

df['date'] = dateutil.parser.parse(df['date'])

错误

AttributeError                            Traceback (most recent call last)
<ipython-input-636-9b19aa5f989c> in <module>()
     15 
     16 # Parse 'Date' Column to Datetime
---> 17 df['date'] = dateutil.parser.parse(df['date'])
     18 
     19 # SELECT RECENT SALES

C:\Python27\lib\site-packages\dateutil\parser.pyc in parse(timestr, parserinfo, **kwargs)
    695         return parser(parserinfo).parse(timestr, **kwargs)
    696     else:
--> 697         return DEFAULTPARSER.parse(timestr, **kwargs)
    698 
    699 

C:\Python27\lib\site-packages\dateutil\parser.pyc in parse(self, timestr, default, ignoretz, tzinfos, **kwargs)
    299             default = datetime.datetime.now().replace(hour=0, minute=0,
    300                                                       second=0, microsecond=0)
--> 301         res = self._parse(timestr, **kwargs)
    302         if res is None:
    303             raise ValueError, "unknown string format"

C:\Python27\lib\site-packages\dateutil\parser.pyc in _parse(self, timestr, dayfirst, yearfirst, fuzzy)
    347             yearfirst = info.yearfirst
    348         res = self._result()
--> 349         l = _timelex.split(timestr)
    350         try:
    351 

C:\Python27\lib\site-packages\dateutil\parser.pyc in split(cls, s)
    141 
    142     def split(cls, s):
--> 143         return list(cls(s))
    144     split = classmethod(split)
    145 

C:\Python27\lib\site-packages\dateutil\parser.pyc in next(self)
    135 
    136     def next(self):
--> 137         token = self.get_token()
    138         if token is None:
    139             raise StopIteration

C:\Python27\lib\site-packages\dateutil\parser.pyc in get_token(self)
     66                 nextchar = self.charstack.pop(0)
     67             else:
---> 68                 nextchar = self.instream.read(1)
     69                 while nextchar == '\x00':
     70                     nextchar = self.instream.read(1)

AttributeError: 'Series' object has no attribute 'read'

---

df['date'].apply(dateutil.parser.parse) 给我错误 AttributeError: 'datetime.date' object has no attribute 'read'

df['date'].truncate(after='2013/04/01') 给出错误 TypeError: can't compare datetime.datetime to long

df['date'].dtype 返回 dtype('O')。它已经是 datetime 对象了吗？

Answer 1

Pandas 知道对象日期时间，但是当您使用某些导入函数时，它会被视为字符串。因此，您需要做的是确保将列设置为日期时间类型而不是字符串。然后，您可以进行查询。

df['date']  = pd.to_datetime(df['date'])
df_masked = df[(df['date'] > datetime.date(2012,4,1)) & (df['date'] < datetime.date(2012,4,4))]