Calculating combinations of subsets of given size leading up to the set

Question

I would like to get all the possible subsets of a given length, that lead up to the real set. So for the set [a,b,c] and subset sizes 1 & 2 I would like to calculate:

[[a,b],[c]] , [[b,c],[a]] , [[a,c],[b]]

I’ve been experimenting with code from Algorithm to calculate power set (all possible subsets) of a set in R , but that algorithm will generate all of the subsets, and not just those leading up to the set.

I’m trying to solve this problem for size ~30. I want to calculate the score of each combination of subsets and only keep the best ones, this way I hope memory is no difficulty. The programming language of choice is python.

Asked By: Maocx

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Source

Answer 1

How about creating the combinations of length 2, and generate the remainder by computing the difference from the original set? Here’s what I mean:

from itertools import combinations

s = {'a', 'b', 'c'}

res = [(set(comb), s.difference(comb)) for comb in combinations(s, 2)]

Generates:

[({'a', 'c'}, {'b'}), ({'b', 'c'}, {'a'}), ({'a', 'b'}, {'c'})]

Answered By: w-m

Answer 2

You can use following code for finding size of subset inside list:

     list1=[[1,2,3],[1,3],[2,3,3,4]]
     x= len(list1)
     while(x>0):
        print len(list1[x-1])
        x=x-1

output:

  4
  2
  3

Answered By: jack

Calculating combinations of subsets of given size leading up to the set

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