python 数据处理中的记录

截取某段时间内的数据，如果以date为index，则：

data.index = pd.to_datetime(data.index)
data = data[(data.index >=pd.to_datetime('20150511')) & (data.index <= pd.to_datetime('20150611'))]

如果Date为column，则：

data['Date'] = pd.to_datetime(data['Date'])
data = data[(data['Date'] >=pd.to_datetime('20120701')) & (data['Date'] <= pd.to_datetime('20120831'))]

 对DataFrame中单个cell进行值的更改，需要遵循先column名，后index的原则，否则无法更改其value

data['crest_price']['2015-04-08']=10  # 要把index写在后面就好

选取某一列的字段以“XXX”开头，产生新的字段

MutualFund.loc[[i.startswith('20010101') for i in MutualFund['s_info_sector']],'level1_type'] = '股票型'
MutualFund.loc[[i.startswith('20010102') for i in MutualFund['s_info_sector']],'level1_type'] = '混合型'

选择数据中，某一columns的值以某一形式开头的数据有两种方法，1、直接选；2、做一个标记选

1、dt = MutualFund.loc[[i.startswith('20010108') for i in MutualFund['s_info_sector']]]

2、MutualFund['wind_investsect'] = [i.startswith('200101') for i in MutualFund['s_info_sector']] 
  MutualFund = MutualFund[MutualFund['wind_investsect']==True]     # 选择投资风格