Merge two dataframes in Python

Question

I have recently started using dataframes in Python and I don't know how can I do the following exercise.

I have two dataframes, both with the same columns ( Type column and Count column) like this:

main_df :

Index	Type	Count
0	Album	12
1	Book	4
2	Person	3

df2 :

Index	Type	Count
0	Album	9
1	Person	4
2	Film	4

Same Type value can have different Index value, as you can see with Type = Person ( Index = 2 in main_df and Index = 1 in df2 ).

I want to have all data in main_df . In this case result will be:

main_df :

Index	Type	Count
0	Album	21
1	Book	4
2	Person	7
3	Film	4

If Type column value in df2 is already in main_df , simply sum the corresponding Count value of df2 . If Type column value in df2 is not in main_df , add that row ( Type and Count value) at the end of main_df .

Hope you can help me with this. Thanks in advance.

Answer 1

You can try with pd.concat and then use groupby :

main_df = pd.concat([main_df,df2]).groupby('Type', sort=False).agg({'Count': sum}).reset_index()

OUTPUT:

     Type  Count
0   Album     21
1    Book      4
2  Person      7
3    Film      4

Answer 2

try via append() , groupby() and sum() :

out=(df1.append(df2)
        .groupby('Type',as_index=False,sort=False)
        .sum())

Output of out :

    Type    Index   Count
0   Album   0       21
1   Book    1       4
2   Person  3       7
3   Film    2       4