Python, itertools.combinations results to different rows in pandas

Question

Lets say I have a list:

list = [1, 2, 3, 4, 5]

I want to get pairwise combinations which are:

[1,2] [1,3] [1,4] [1,5] [2,3] [2,4] [2,5] [3,4] [3,5] [4,5]

Then I want to save the output to rows in pandas. Resulting output should look like this:

     Combinations
0  [[1,2],[1,3],[1,4],[1,5]]
1  [[2,3],[2,4],[2,5]]
2  [[3,4], [3,5]]
3  [[4,5]]

I have to do it for a list which consists of 1000 elements. Any help will be highly appreciated

Answer 1

You can group the pairs by their first element:

from itertools import combinations, groupby
from pandas import Series
from operator import itemgetter

combined = combinations(inputlist, 2)
series = Series(list(g) 
                for k, g in groupby(combined, key=itemgetter(0)))

Demo:

>>> from itertools import combinations, groupby
>>> from pandas import Series
>>> from operator import itemgetter
>>> inputlist = [1, 2, 3, 4, 5]
>>> combined = combinations(inputlist, 2)
>>> Series(list(g) for k, g in groupby(combined, key=itemgetter(0)))
0    [(1, 2), (1, 3), (1, 4), (1, 5)]
1            [(2, 3), (2, 4), (2, 5)]
2                    [(3, 4), (3, 5)]
3                            [(4, 5)]
dtype: object