Sum the columns of two dataframes of different length

Question

I have two dataframes：

df1

    country  value
0      aa      1
1      bb      1
2      cc      5

df2

     country  value
0      cc      8
1      aa      2
2      MM      1
3      FF      6

How get I can this dataframe ( df1 + df2 ) as follows:

    country  value
0      aa      3
1      bb      1
2      MM      1
3      cc      13
4      FF      6

Answer 1

Use set_index and add with fill_value=0 :

df1.set_index('country').add(df2.set_index('country'),fill_value=0).reset_index()

Output:

  country  value
0      FF    6.0
1      MM    1.0
2      aa    3.0
3      bb    1.0
4      cc   13.0

Answer 2

You can first concatenate using pd.concat , then use df.groupby :

In [390]: pd.concat([df, df2]).groupby('country', as_index=False).sum()
Out[390]: 
  country  value
0      FF      6
1      MM      1
2      aa      3
3      bb      1
4      cc     13