数据框警告:Python中的SettingWithCopyWarning

问题描述

正在处理来自
的文件 http://portal.amfiindia.com/spages/NAV0.txt
获得如下输出:
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，
..
..
..

Processing file from
http://portal.amfiindia.com/spages/NAV0.txt
to get output as follows:
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.

I have tried using below code but getting below warning.

代码:

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:13: SettingWithCopyWarning:试图在一个副本上设置一个值 从DataFrame切片.尝试使用.loc [row_indexer，col_indexer] = 值代替

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:试图在一个副本上设置一个值 从DataFrame切片.尝试使用.loc [row_indexer，col_indexer] = 值代替

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:试图在一个副本上设置一个值 从DataFrame切片.尝试使用.loc [row_indexer，col_indexer] = 值代替

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:试图在一个副本上设置一个值 从DataFrame切片.尝试使用.loc [row_indexer，col_indexer] = 值代替

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:试图在一个副本上设置一个值 从DataFrame切片.尝试使用.loc [row_indexer，col_indexer] = 值代替

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:试图在一个副本上设置一个值 从DataFrame切片.尝试使用.loc [row_indexer，col_indexer] = 值代替

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['Net Asset Value'],errors='coerce').map(lambda x: '%2.7f' % x]
但这没有帮助.
帮助将不胜感激.

Csv file is getting generated as expected but how can I overcome this warning?I have tried using
fil_df.loc[ pandas.to_numeric(fil_df['Net Asset Value'],errors='coerce').map(lambda x: '%2.7f' % x]
but it didnt help.
Help would be appreciated.

推荐答案

我认为您需要添加 copy :

I think you need add copy:

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

如果以后在fil_df中修改值，您会发现修改不会传播回原始数据(df)，并且Pandas会发出警告.

If you modify values in fil_df later you will find that the modifications do not propagate back to the original data (df), and that Pandas does warning.

这篇关于数据框警告:Python中的SettingWithCopyWarning的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！