Pandas Groupy take only the first N Groups [duplicate]

Question

I have some DataFrame which I want to group by the ID, e. g.:

import pandas as pd
df = pd.DataFrame({'item_id': ['a', 'a', 'b', 'b', 'b', 'c', 'd'], 'user_id': [1,2,1,1,3,1,5]})
print df

Which generates:

  item_id  user_id
0       a        1
1       a        2
2       b        1
3       b        1
4       b        3
5       c        1
6       d        5

[7 rows x 2 columns]

I can easily group by the id:

grouped = df.groupby("item_id")

But how can I return only the first N group-by objects? E. g. I want only the first 3 unique item_ids.

Answer 1

Here is one way using list(grouped).

result = [g[1] for g in list(grouped)[:3]]

# 1st
result[0]

  item_id  user_id
0       a        1
1       a        2

# 2nd
result[1]

  item_id  user_id
2       b        1
3       b        1
4       b        3