大熊猫指定一个用notnull（）过滤的系列，(Pandas Assigning back a series that was filtered with notnull())

 各位开发人员， 
 
 我目前正在学习大熊猫，并且仍然试图围绕如何分配值，我将其转换为特定类型，例如回到原始数据框。 
 
 更具体的我有这个数据框： 
 
     id         A       B
0   50000    12413     32885.0
1   50001     2040     43737.0
3   50002     2040     28015.0
4   50003     2040      NaN
5   50004     2040     28565.0
 
 我的目标是将B列转换为整数，但保留NaN值，因此没有fillna(0) 。 我想要这个： 
 
     id         A       B
0   50000    12413     32885
1   50001     2040     43737
3   50002     2040     28015
4   50003     2040      NaN
5   50004     2040     28565
 
 我用print(df.loc[df['B'].notnull(), 'B'].astype('int'))做了这个print(df.loc[df['B'].notnull(), 'B'].astype('int'))并且它有效。 
 
        B
0   32885
1   43737
3   28015
4   28565
 
 但是，如果我尝试将其分配回数据帧蒙山： 
 
df.loc[df['B'].notnull(), 'B'] = df.loc[df['B'].notnull(), 'B'].astype('int')
 
 我仍然得到原始的，未转换的数据。 所以我似乎做错了任务，但我无法弄清楚如何正确地做到这一点。 帮助将非常感谢！ 

Hello fellow developers,
 
I am currently learning pandas and still trying to wrap my head around how to assign values, that I converted to a specific type for example, back to the origin dataframe.
 
More specific I have this dataframe:
 
     id         A       B
0   50000    12413     32885.0
1   50001     2040     43737.0
3   50002     2040     28015.0
4   50003     2040      NaN
5   50004     2040     28565.0
 
My goal is to convert column B to integers but leave NaN values as is, so no fillna(0). I want to have this:
 
     id         A       B
0   50000    12413     32885
1   50001     2040     43737
3   50002     2040     28015
4   50003     2040      NaN
5   50004     2040     28565
 
I did this with print(df.loc[df['B'].notnull(), 'B'].astype('int')) and it worked.
 
        B
0   32885
1   43737
3   28015
4   28565
 
But if I try to assign it back to the data frame whith:
 
df.loc[df['B'].notnull(), 'B'] = df.loc[df['B'].notnull(), 'B'].astype('int')
 
I still get the original, unconverted data. So I seem to do the assignment wrong, but I can't figure out how to do it correctly. Help would be much appreciated!

原文：https://stackoverflow.com/questions/50603794