Python pandas 使用dataframe操作时出现警告

Question

final_merge['user_ID']=''
for i in range(len(final_merge)):
    if final_merge.loc[i,'user_x']=='nan':
        final_merge['user_ID'][i]= final_merge['user_y'][i]
    else:
        final_merge['user_ID'][i]= final_merge['user_x'][i]

当我使用代码时，我的控制台中有两个警告。

__main__:6: SettingWithCopyWarning: 
A value is trying to be set on a copy of a slice from a DataFrame

See the caveats in the documentation: http://pandas.pydata.org/pandas-docs/stable/indexing.html#indexing-view-versus-copy
__main__:4: SettingWithCopyWarning: 
A value is trying to be set on a copy of a slice from a DataFrame

See the caveats in the documentation: http://pandas.pydata.org/pandas-docs/stable/indexing.html#indexing-view-versus-copy

我知道警告的意思，但是如何更改我的代码以避免这些警告？

Answer 1

这与 SettingWithCopyWarning 有关，同样在 pandas 中，对于这种情况，我们通常有多种方式而不是 for 循环

np.where

final_merge['user_ID']=np.where(final_merge['user_x']=='nan',final_merge['user_y'],final_merge['user_x'])

或fillna，如果nan是np.nan，如果不是final_merge['user_x'].replace('nan',np.nan, inplace=True)

final_merge['user_ID']=final_merge['user_x'].fillna(final_merge['user_y'])

或mask

final_merge['user_ID']=final_merge['user_x'].mask(final_merge['user_x']=='nan',final_merge['user_y'])

Python pandas 使用dataframe操作时出现警告

Python pandas appear warning when use dataframe operation

python

warnings

dataframe

pandas