Aggregate dataframe indices in python

Question

I want to aggregate indices of a dataframe with groupby function.

     word  count
0    a     3
1    the   5
2    a     3
3    an    2
4    the   1

What I want is a pd.Series which consists of list(descending order) of indices,

word
a       [2, 0]
an         [3]
the     [4, 1]

I've tried some built-in functions with groupby, however, I couldn't find a way to aggregate indices. Would you like to provide any hint or solution for this problem?

@IanS Well yes. For this question, those columns are useless. I just put it to emphasize the data is a dataframe. — SUNDONG
– SUNDONG, Commented Sep 22, 2016 at 12:20

jezrael · Accepted Answer · 2016-09-22 12:24:27Z

3

I think you can first change order of index by [::-1], then groupby and apply index to list. Last sort_index:

print (df[::-1].groupby('word', sort=False).apply(lambda x: x.index.tolist()).sort_index())
word
a      [2, 0]
an        [3]
the    [4, 1]
dtype: object

Another similar solution:

print (df.sort_index(ascending=False)
         .groupby('word', sort=False)
         .apply(lambda x: x.index.tolist())
         .sort_index())
word
a      [2, 0]
an        [3]
the    [4, 1]
dtype: object

edited Sep 22, 2016 at 12:24

answered Sep 22, 2016 at 12:19

jezrael

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2 Comments

SUNDONG Over a year ago

Thank you very much. I need to get used to lambda function!

jezrael Over a year ago

Glad can help you!

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