将频率“MS”设置为熊猫日期时间对象 - python

Posted 2023-03-12

【中文标题】将频率“MS”设置为熊猫日期时间对象 - python

【英文标题】：Set frequency 'MS' to pandas datatime object - python

【发布时间】：2020-08-31 04:14:09

【问题描述】：

我在 pandas 中有这个数据框：

df = pd.read_csv('data_stack.csv',index_col='month',parse_dates=True)

如果我查看参数freq，它会自动推断为无

DatetimeIndex(['2018-09-01', '2018-08-01', '2018-07-01', '2018-06-01',
               '2018-05-01', '2018-04-01', '2018-03-01', '2018-02-01',
               '2018-01-01', '2017-12-01',
               ...
               '2018-11-01', '2019-01-01', '2018-12-01', '2018-11-01',
               '2019-01-01', '2018-12-01', '2018-11-01', '2019-01-01',
               '2018-12-01', '2018-11-01'],
              dtype='datetime64[ns]', name='month', length=4325, freq=None)

我想把它写成每月开始的“MS”：

df.index.freq = 'MS'

但我收到此错误：

ValueError                                Traceback (most recent call last)
<ipython-input-99-0dc1e7b74d6b> in <module>
----> 1 df.index.freq = 'MS'

~/opt/anaconda3/lib/python3.7/site-packages/pandas/core/indexes/extension.py in fset(self, value)
     64 
     65             def fset(self, value):
---> 66                 setattr(self._data, name, value)
     67 
     68             fget.__name__ = name

~/opt/anaconda3/lib/python3.7/site-packages/pandas/core/arrays/datetimelike.py in freq(self, value)
    925         if value is not None:
    926             value = frequencies.to_offset(value)
--> 927             self._validate_frequency(self, value)
    928 
    929         self._freq = value

~/opt/anaconda3/lib/python3.7/site-packages/pandas/core/arrays/datetimelike.py in _validate_frequency(cls, index, freq, **kwargs)
   1001             #  message.
   1002             raise ValueError(
-> 1003                 f"Inferred frequency inferred from passed values "
   1004                 f"does not conform to passed frequency freq.freqstr"
   1005             )

ValueError: Inferred frequency None from passed values does not conform to passed frequency MS

我找了类似的案例，找到了这个：pandas.DatetimeIndex frequency is None and can't be set

我试过了，但我得到了同样的错误，谁能告诉我为什么？

数据在这个存储库中：https://github.com/jordi-crespo/stack-questions

【参考方案1】：

没有频率，因为您的索引中有重复值。所以我想你可以用这样一个索引来设置频率的唯一事情就是以某种方式聚合数据，例如

>>> df.resample('MS').mean().index
DatetimeIndex(['2017-01-01', '2017-02-01', '2017-03-01', '2017-04-01',
               '2017-05-01', '2017-06-01', '2017-07-01', '2017-08-01',
               '2017-09-01', '2017-10-01', '2017-11-01', '2017-12-01',
               '2018-01-01', '2018-02-01', '2018-03-01', '2018-04-01',
               '2018-05-01', '2018-06-01', '2018-07-01', '2018-08-01',
               '2018-09-01', '2018-10-01', '2018-11-01', '2018-12-01',
               '2019-01-01'],
              dtype='datetime64[ns]', name='month', freq='MS')

它为您提供所需频率的索引。但我不确定这是否是你真正想要的。