From: "Jan E." <lists@...>
Date: 2012-04-12T18:15:34+09:00
Subject: Re: ruby v.1.8.6. Expand array class, make combinations

Hi,

What do you mean by "use newarr"? If you want the method to return the 
result array, you have to write "return newarr" (or simply "newarr") in 
the method body:

class Array
  def comby  ## Make al unique combinations of 2 elements
     posmax = (length - 1)
     newarr = []
     for n in 0.. posmax
      for m in 0.. posmax
        i1 = self[n]
        i2 = self[m]
        if  newarr.include? ([i2,i1])
           # newarr.push('X')
        elsif i1 == i2
            # newarr.push('X')
        else
           newarr.push([i1,i2])
        end
      end
     end
     newarr  # return the result array
  end
end

By the way, I would replace the "for ... in" loops with "upto" 
iterators. Those or more Ruby-like and have the advantage of not 
spilling every internal variable. And the inner loop/iterator shouldn't 
start at 0 but at the next to current index of the outer loop/iterator. 
Then you can leave out the if statement (assuming the base array is 
unique):

0.upto posmax do |i|
  (i + 1).upto posmax do |j|
     newarr << [self[i], self[j]]
  end
end

-- 
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