How to get groupby sum of multiple columns

Question

I have a pandas dataframe which looks like this:

index col1   col2   col3   col4   col5
0     a      c      1      2      f 
1     a      c      1      2      f
2     a      d      1      2      f
3     b      d      1      2      g
4     b      e      1      2      g
5     b      e      1      2      g

I want to group by col1 and col2 and get the sum() of col3 and col4. col5 can be dropped since the data can not be aggregated.

Here is what the output should look like. I am interested in having both col3 and col4 in the resulting dataframe. It doesn’t really matter if col1 and col2 are part of the index or not.

index col1   col2   col3   col4   
0     a      c      2      4          
1     a      d      1      2      
2     b      d      1      2      
3     b      e      2      4

Here is what I tried:

df_new = df.groupby(['col1', 'col2'])['col3', 'col4'].sum()

That however only returns the aggregated results of col4.

How do I make it work?

Asked By: Axel

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Source

Answer 1

By using apply

df.groupby(['col1', 'col2'])["col3", "col4"].apply(lambda x : x.astype(int).sum())
Out[1257]: 
           col3  col4
col1 col2            
a    c        2     4
     d        1     2
b    d        1     2
     e        2     4

If you want to agg

df.groupby(['col1', 'col2']).agg({'col3':'sum','col4':'sum'})

Answered By: BENY

Answer 2

The issue is likely that df.col3.dtype is likely not an int or a numeric datatype. Try df.col3 = df.col3.astype(int) before doing your groupby

Additionally, select your columns after the groupby to see if the columns are even being aggregated:

df_new = df.groupby(['col1', 'col2']).sum()[["col3", "col4"]]

Answered By: A.Kot

Answer 3

The above answer didn’t work for me.

df_new = df.groupby(['col1', 'col2']).sum()[["col3", "col4"]]

I was grouping by single group by and sum columns.

Here is the one worked for me.

D1.groupby(['col1'])['col2'].sum() << The sum at the end not the middle.

Answered By: Leo James

Answer 4

Another generic solution is

df.groupby(['col1','col2']).agg({'col3':'sum','col4':'sum'}).reset_index()

This will give you the required output.

UPDATED (June 2020):
Introduced in Pandas 0.25.0, Pandas has added new groupby behavior “named aggregation” and tuples, for naming the output columns when applying multiple aggregation functions to specific columns.

df.groupby(['col1','col2']).agg(
     sum_col3 = ('col3','sum'),
     sum_col4 = ('col4','sum'),
     ).reset_index()

Also, you can name new columns, e.g. I’ve used ‘sum_col3’ and ‘sum_col4’, but you can use any name you want.

Refer to Link for detailed description.

Answered By: Prateek Sharma

Answer 5

I think it would be more efficient to do the following:

df.groupby(['col1', 'col2']).agg({'col3':'sum','col4':'sum'}).sum(axis=1)

or:

df.groupby(['col1', 'col2'])['col3', 'col4'].sum().sum(axis=1)

This does assume you have appropriate types in the dataframe.

Answered By: Hanni Ali

Answer 6

Due to pandas FutureWarning: Indexing with multiple keys discussed on GitHub and Stack Overflow, I recommend this solution:

df.groupby(['col1', 'col2'])[['col3', 'col4']].sum().reset_index()

Output:

Answered By: oil_lamp

Answer 7

You miss a pair of square brackets to select necessary columns in your DataFrameGroupBy object:

df.groupby(['col1', 'col2'])[['col3', 'col4']].sum()

You can also drop columns you don’t need before groupby:

df.drop('col5', axis=1).groupby(['col1', 'col2']).sum()

Answered By: Mykola Zotko

How to get groupby sum of multiple columns

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