熊猫-根据另一列的行总数创建新列的正确方法（试图在副本上设置的值）？

Question

I have a dataframe with dates, names, and values, and all I want to do is create a column that is the output of the total sum of values by date, then subtract that sum by the value for each name for that date. I've been able to do this, but am getting the common error: A value is trying to be set on a copy of a slice from a DataFrame.

This is my code: df['ex_Term'] = df.groupby('name').Term.transform('sum') - df['Term']

It's telling me to use the iloc function and after reading the documentation and trying this code, it still didn't work: df['ex_Term'] = df.groupby('name').loc[:,('Term')].sum()- df['Term']

example df:

 name   Country   value   delta  
 mike   UK            1      -1  
 mike   US            2       1  

Answer 1

IIUC尝试使用assgin

df=df.assgin(ex_Term=df.groupby('name').Term.transform('sum') - df['Term'])