Function translation to find all sections of a collection from Python to Ruby

Question

I have the following python function to recursively search all sections of a set:

def partitions(set_): if not set_: yield [] return for i in xrange(2**len(set_)/2): parts = [set(), set()] for item in set_: parts[i&1].add(item) i >>= 1 for b in partitions(parts[1]): yield [parts[0]]+b for p in partitions(["a", "b", "c", "d"]): print(p) 

Can someone help me convert this to ruby? This is what I still have:

 def partitions(set) if not set yield [] return end (0...2**set.size/2).each { |i| parts = [Set.new, Set.new] set.each { |item| parts[i&1] << item i >>= 1 } partitions(parts[1]).each { |b| yield [parts[0]] << b } } end p partitions([1, 2, 3, 4].to_set) 

I get the error "LocalJumpError: no block". I think this is because yield functions work differently in Python and Ruby.

Answer 1

 #!/usr/bin/ruby1.8 def partitions(set) yield [] if set.empty? (0 ... 2 ** set.size / 2).each do |i| parts = [[], []] set.each do |item| parts[i & 1] << item i >>= 1 end partitions(parts[1]) do |b| result = [parts[0]] + b result = result.reject do |e| e.empty? end yield result end end end partitions([1, 2, 3, 4]) do |e| pe end # => [[1, 2, 3, 4]] # => [[2, 3, 4], [1]] # => [[1, 3, 4], [2]] # => [[3, 4], [1, 2]] # => [[3, 4], [2], [1]] # => [[1, 2, 4], [3]] # => [[2, 4], [1, 3]] # => [[2, 4], [3], [1]] # => [[1, 4], [2, 3]] # => [[1, 4], [3], [2]] # => [[4], [1, 2, 3]] # => [[4], [2, 3], [1]] # => [[4], [1, 3], [2]] # => [[4], [3], [1, 2]] # => [[4], [3], [2], [1]] 

What else:

• Defender calls set.empty? instead of (implicitly) testing for set.nil?
• Leave a .each message when calling the Partition
• Use array instead of Set
• Filter empty sets from the result

Answer 2

You will need to think of Ruby yield as a call to a custom operation.

 def twice yield yield end twice { puts "Hello" } 

Therefore, whenever your code gives a value, the processing function for this element will be called.

 partitions([1, 2, 3, 4].to_set) { |result| # process result } 

This code does not generate a list at all.