Data_Frame Error – ValueError: Can only compare identically-labeled Series objects

I have two data_frames, as below:

df_name:
   Student_ID  Name        DOB
0           1  Raju 1993-02-02
1           2  Indu 1987-01-04
2           3  Laya 2000-06-24

df_marks:
    Student_ID Subject  Int1/40  Int2/40
0            1     Eng       10       35
1            1     Tam       30       38
2            1     Mat       20       30
3            1     Sci       15       20
4            2     Eng       35       25
5            2     Tam       25       15
6            2     Mat       22       30
7            2     Sci       29       23
8            3     Eng       18       17
9            3     Tam       19       16
10           3     Mat       27       26

The task is to create a data_frame(below one), where I need to add df_marks['Int1/40'] & df_marks['Int2/40'], if df_name['Student_ID'] == df_marks['Student_ID']

   Student_id  Name        DOB  Tam/50
0           1  Raju 1993-02-02     NaN
1           2  Indu 1987-01-04     NaN  
2           3  Laya 2000-06-24     NaN

I tried

df_out['Tam/50'] = df_marks[['Int1/40','Int2/40']].sum(axis=1).where(df_marks['Subject']==df_out['Student_id'])

But its giving error as,

ValueError: Can only compare identically-labeled Series objects

Do we have any simple way to do this?

Regards, Deepak Dash

Answer

Use DataFrame.join with aggregated sum for new column in df_name:

df_marks['Tam/50'] = df_marks[['Int1/40','Int2/40']].sum(axis=1)
df_name = df_name.join(df_marks.groupby('Student_ID')['Tam/50'].sum(), on='Student_ID')
print (df_name)
   Student_ID  Name         DOB  Tam/50
0           1  Raju  1993-02-02     198
1           2  Indu  1987-01-04     204
2           3  Laya  2000-06-24     123

Or solution without helper column:

s = (df_marks[['Int1/40','Int2/40']].sum(axis=1)
                                    .groupby(df_marks['Student_ID'])
                                    .sum()
                                    .rename('Tam/50'))

df_name = df_name.join(s, on='Student_ID')
print (df_name)
   Student_ID  Name         DOB  Tam/50
0           1  Raju  1993-02-02     198
1           2  Indu  1987-01-04     204
2           3  Laya  2000-06-24     123