数据框警告：Python中的SettingWithCopyWarning

正在处理来自的文件
http://portal.amfiindia.com/spages/NAV0.txt
得到如下输出：
31012017,1,1,135765,12,10.8536000,
31012017,1,1,135762,12,10.8543000,
31012017,1,1,135760,12,10.6599000,
31012017,1,1,135759,12,10.6554000,
31012017,1,1,135763,12,10.8536000,
..
..
..

我尝试使用下面的代码,但得到警告以下.

码：

import pandas
import numpy as np

#Sample file for NAV0.txt can be downloaded from url: http://portal.amfiindia.com/spages/NAV0.txt
#creating pandas with selected columns
df=pandas.read_table('NAV0.txt',sep=';',usecols=['Date','Scheme Code','Net Asset Value'])

#converting column with name 'Scheme Code' to digit to remove string part
fil_df=df[df['Scheme Code'].apply(lambda x : str(x).isdigit())]

#converting column with name 'Net Asset value' to numberic and set each value with 7 decimal places 
fil_df['Net Asset Value']=pandas.to_numeric(fil_df['Net Asset Value'],errors='coerce')
fil_df['Net Asset Value']=fil_df['Net Asset Value'].map(lambda x: '%2.7f' % x)


#Formating Date column as YYYMMDD
fil_df['Date']=pandas.to_datetime(fil_df['Date']).dt.strftime('%d%m%Y')

#adding extra column in dataframe
fil_df['ser1']=1
fil_df['ser2']=1
fil_df['period']=12
fil_df['lcol']=''
fil_df=fil_df[['Date','ser1','ser2','Scheme Code','period','Net Asset Value','lcol']]

#Converting datafile to csv
fil_df.to_csv('NAV_1.csv',index=False,header=None)
fil_df.dtypes

错误：

c:\users\administrator\appdata\local\programs\python\python35-32\lib\site-packages\ipykernel__main__.py:12:
SettingWithcopyWarning: A value is trying to be set on a copy of a
slice from a DataFrame. Try using .loc[row_indexer,col_indexer] =
value instead

c:\users\administrator\appdata\local\programs\python\python35-32\lib\site-packages\ipykernel__main__.py:13:
SettingWithcopyWarning: A value is trying to be set on a copy of a
slice from a DataFrame. Try using .loc[row_indexer,col_indexer] =
value instead

c:\users\administrator\appdata\local\programs\python\python35-32\lib\site-packages\ipykernel__main__.py:17:
SettingWithcopyWarning: A value is trying to be set on a copy of a
slice from a DataFrame. Try using .loc[row_indexer,col_indexer] =
value instead

c:\users\administrator\appdata\local\programs\python\python35-32\lib\site-packages\ipykernel__main__.py:20:
SettingWithcopyWarning: A value is trying to be set on a copy of a
slice from a DataFrame. Try using .loc[row_indexer,col_indexer] =
value instead

c:\users\administrator\appdata\local\programs\python\python35-32\lib\site-packages\ipykernel__main__.py:21:
SettingWithcopyWarning: A value is trying to be set on a copy of a
slice from a DataFrame. Try using .loc[row_indexer,col_indexer] =
value instead

c:\users\administrator\appdata\local\programs\python\python35-32\lib\site-packages\ipykernel__main__.py:22:
SettingWithcopyWarning: A value is trying to be set on a copy of a
slice from a DataFrame. Try using .loc[row_indexer,col_indexer] =
value instead

c:\users\administrator\appdata\local\programs\python\python35-32\lib\site-packages\ipykernel__main__.py:23:
SettingWithcopyWarning: A value is trying to be set on a copy of a
slice from a DataFrame. Try using .loc[row_indexer,col_indexer] =
value instead

CSV文件已按预期生成,但是如何克服此警告？
我尝试使用
fil_df.loc [pandas.to_numeric(fil_df [‘净资产值’],errors =’coerce’).map(lambda x：’％2.7f’％x]
但它没有帮助.
帮助将不胜感激.

解决方法:

我认为您需要添加copy：

fil_df=df[df['Scheme Code'].apply(lambda x : str(x).isdigit())].copy()

如果以后再修改fil_df中的值,您将发现修改不会传播回原始数据(df),并且Pandas会发出警告.