pandas: get all groupby values in an array [duplicate]

Question

I'm sure this has been asked before, sorry if duplicate. Suppose I have the following dataframe:

df = pd.DataFrame({'key': ['A', 'B', 'C', 'A', 'B', 'C'],
                   'data': range(6)}, columns=['key', 'data'])

>>
    key data
0   A   0
1   B   1
2   C   2
3   A   3
4   B   4
5   C   5

Doing a groupby on 'key', df.groupby('key').sum() I know we can do things like:

>> 
    data
key 
A   3
B   5
C   7

What is the easiest way to get all the 'splitted' data in an array?:

>> 
    data
key 
A   [0, 3]
B   [1, 4]
C   [2, 5]

I'm not necessarily grouping by just one key, but with several other indexes as well ('year' and 'month' for example) which is why I'd like to use the groupby function, but preserve all the grouped values in an array.

anky · Accepted Answer · 2019-03-12 15:53:09Z

31

You can use apply(list):

print(df.groupby('key').data.apply(list).reset_index())

  key    data
0   A  [0, 3]
1   B  [1, 4]
2   C  [2, 5]

answered Mar 12, 2019 at 15:53

community wiki

anky

Sign up to request clarification or add additional context in comments.

8 Comments

ru111 Over a year ago

For arrays instead of lists you can do df.groupby('key').data.apply(np.array) which was more convenient for my operations.

anky Over a year ago

@Moondra df.groupby("Column Name").agg(list) should help.. another way is pivot table (not required though) df.pivot_table(index="Column Name",aggfunc=list)

Nischaya Sharma Over a year ago

Hey, I am getting the error Error:'DataFrameGroupBy' object has no attribute 'data'. My line of code is main_group = main.groupby(["new-date", 'seller_identifier', 'affiliate_name']).data.apply(np.array).reset_index() Any solutions to this?

anky Over a year ago

@NischayaSharma remove the .data from your code and try

futurulus Over a year ago

@NischayaSharma I ran into this also, and it took me way longer than it should have to figure it out: .data is a column name, not a Pandas API field. You'll get 'DataFrameGroupBy' object has no attribute 'data' if your DataFrame has different column names, and the solution is just to replace data with the name of your actual column.

|

Collectives™ on Stack Overflow

pandas: get all groupby values in an array [duplicate]

1 Answer 1

8 Comments

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

8 Comments

Linked

Related