Python: Pandas dataframe sum

Question

I try to learn how to work with pandas dataframes. My dataframe has 4 columns A,B,C,D.

For index (A,B,C) there are multiple values of D. I want to merge these rows and sum the values of D.

I have:

╔═══╦═══╦═══╦═══╦═══╗
║   ║ A ║ B ║ C ║ D ║   
╠═══╬═══╬═══╬═══╬═══╣
║ 1 ║ 1 ║ 2 ║ 3 ║ 5 ║
║ 1 ║ 1 ║ 2 ║ 3 ║ 3 ║
║ 2 ║ 1 ║ 5 ║ 4 ║ 2 ║
║ 2 ║ 1 ║ 2 ║ 4 ║ 2 ║
║ 3 ║ 1 ║ 2 ║ 4 ║ 2 ║
║ 3 ║ 1 ║ 2 ║ 4 ║ 3 ║
╚═══╩═══╩═══╩═══╩═══╝

I want to get:

╔═══╦═══╦═══╦═══╦═══╗
║   ║ A ║ B ║ C ║ D ║
╠═══╬═══╬═══╬═══╬═══╣
║ 1 ║ 1 ║ 2 ║ 3 ║ 8 ║
║ 2 ║ 1 ║ 5 ║ 4 ║ 2 ║
║ 2 ║ 1 ║ 2 ║ 4 ║ 2 ║
║ 3 ║ 1 ║ 2 ║ 4 ║ 5 ║
╚═══╩═══╩═══╩═══╩═══╝

I tried to do it this way:

df=df.groupby(['A','B','C'])['D'].sum()

But it gives me a Series instead.

so are you wanting df=df.groupby(['A','B','C'])['D'].sum().reset_index() or df=df.groupby(['A','B','C'], as_index=False)['D'].sum() — EdChum
– EdChum, Commented Jun 29, 2016 at 7:39
Yes it works :) you can put it into answer and I will mark it as solved — SpeedEX505
– SpeedEX505, Commented Jun 29, 2016 at 7:41

EdChum · Accepted Answer · 2016-06-29 07:47:56Z

1

If you want to retain the columns after groupby you can call reset_index:

In [185]:
df.groupby(['A','B','C'])['D'].sum().reset_index()

Out[185]:
   A  B  C  D
0  1  2  3  8
1  1  2  4  7
2  1  5  4  2

or pass arg as_index=False

answered Jun 29, 2016 at 7:47

EdChum

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