Comments on: Creating Combinations of Sets/Arrays/Things in Ruby http://www.semergence.com/2007/03/27/creating-combinations-of-setsarraysthings-in-ruby/ Semantic Web, Ruby on Rails, and Massive Data Fri, 21 Nov 2008 00:06:23 +0000 http://wordpress.org/?v=2.2.3 By: Brian Adkins http://www.semergence.com/2007/03/27/creating-combinations-of-setsarraysthings-in-ruby/#comment-233 Brian Adkins Mon, 10 Sep 2007 18:12:30 +0000 http://www.semergence.com/2007/03/27/creating-combinations-of-setsarraysthings-in-ruby/#comment-233 <p>BTW you can combine your first and third line since they both have 'k==0' and both return [[]]</p> BTW you can combine your first and third line since they both have ‘k==0′ and both return [[]]

]]> By: Brian Adkins http://www.semergence.com/2007/03/27/creating-combinations-of-setsarraysthings-in-ruby/#comment-232 Brian Adkins Mon, 10 Sep 2007 18:10:05 +0000 http://www.semergence.com/2007/03/27/creating-combinations-of-setsarraysthings-in-ruby/#comment-232 <p>boy that looks bad! Maybe you can wrap the code with <pre></p> boy that looks bad! Maybe you can wrap the code with <pre>

]]> By: Brian Adkins http://www.semergence.com/2007/03/27/creating-combinations-of-setsarraysthings-in-ruby/#comment-231 Brian Adkins Mon, 10 Sep 2007 18:09:22 +0000 http://www.semergence.com/2007/03/27/creating-combinations-of-setsarraysthings-in-ruby/#comment-231 <p>Here's an alternative version. I'm still not real pleased with it. I don't like the inefficiency of slicing the array repeatedly, but probably the only way to avoid that is to use a set of indices to navigate through the array which would clutter things up.</p> Return all combinations of n elements from array combinations([1,2,3],2) -> [[1,2],[1,3],[2,3]] <p>def combinations array, n result = [] if n > 0 (0 .. array.length - n).each do |i| combs = combinations(array[i + 1 .. -1], n - 1) combs = [[]] if combs.empty? combs.collect {|comb| [array[i]] + comb}.each {|x| result << x} end end return result end</p> Here’s an alternative version. I’m still not real pleased with it. I don’t like the inefficiency of slicing the array repeatedly, but probably the only way to avoid that is to use a set of indices to navigate through the array which would clutter things up.

Return all combinations of n elements from array

combinations([1,2,3],2) -> [[1,2],[1,3],[2,3]]

def combinations array, n
result = []
if n > 0
(0 .. array.length - n).each do |i|
combs = combinations(array[i + 1 .. -1], n - 1)
combs = [[]] if combs.empty?
combs.collect {|comb| [array[i]] + comb}.each {|x| result << x}
end
end
return result
end

]]>