How can I combine arrays in Python?

Question

I have the following:

[[1, 2], [3], [4,5], [6,1], [5,3,4], [4,7]]

I'm trying to combine these so that if a number is in another array, I combine the arrays. The output should be this:

[[1,2,6],[3,4,5,7]]

Any ideas on how I can do this in Python?

It is not clear what you mean by "if the number is in another array". If what number is in another array? — merlin2011, Apr 09 '14 at 21:45
@merlin2011, I think its if two of the sublists share a common number, the should be combined — wnnmaw, Apr 09 '14 at 21:45
Does the output have to be sorted? Also it looks like you want to remove duplicates. You can use sets instead. — Scorpion_God, Apr 09 '14 at 21:47
@crclayton - yes that's what I'm looking for. Sorry for the duplicate. — myname, Apr 09 '14 at 21:50

score 0 · Accepted Answer · answered Apr 09 '14 at 21:52

Here's what I'd do:

>>> L = [[1, 2], [3], [4,5], [6,1], [5,3,4], [4,7]]
>>> L = [set(e) for e in L]
>>> combined = []
>>> while L:
...     group = L.pop()
...     for other in L:
...         if group.intersection(other):
...             group.update(other)
...     L = [e for e in L if not group.intersection(e)]
...     combined.append(group)
... 
>>> combined
[set([3, 4, 5, 7]), set([1, 2, 6])]

This first converts each group in the original list to set, then greedily merges the elements together into groups.

Just about to post this, but you beat me to it. – Scorpion_God Apr 09 '14 at 21:59 — Scorpion_God, Apr 09 '14 at 21:59

How can I combine arrays in Python?

1 Answers1