Ruby v.1.8.6. Expand array class, make combinations

ruby-talk
1

Hi,

I'm using Sketchups' ruby; its version: 1.8.6. Sketchup is a 3D design
program which has as ruby built in to perform all kinds of operations on
geometry.I'm not able to use higher versions of ruby.

My question:

This is what I want to accomplish:

["a","b","c","d"].permutation(2)

==> [ [a,b],[a,c],[a,d],[b,c],[b,d],[c,d] ]
but it's not available for me

I also found:

http://permutation.rubyforge.org/. I succeeded to install the gem,
but I couldn't accomplish the above.

So I've created my own method:

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
    puts newarr[0..14]
                ==> [ [a,b],[a,c],[a,d],[b,c],[b,d],[c,d] ]

  end

end

//program

mm = ["a","b","c","d"]

mm.comby

//

It puts the right values, but what I can't use newarr ( tried also
@newarr)
in my program.

What would like to see:

mm = ["a","b","c","d"]
aa = mm.comby
puts aa
==> [ [a,b],[a,c],[a,d],[b,c],[b,d],[c,d] ]

What can I do??

Thanks!

···

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2

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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3

What about ruby facets: http://rubyworks.github.com/rubyfaux/?doc=http://rubyworks.github.com/facets/docs/facets-2.9.3/core.json#api-class-Array/api-method-Array-h-combination

There is a combination method for the Array class. does it fit your needs?

ralf

···

On 04/12/2012 10:10 AM, Ronnie Aa wrote:

Hi,

I'm using Sketchups' ruby; its version: 1.8.6. Sketchup is a 3D design
program which has as ruby built in to perform all kinds of operations on
geometry.I'm not able to use higher versions of ruby.

My question:

This is what I want to accomplish:

["a","b","c","d"].permutation(2)

==> [ [a,b],[a,c],[a,d],[b,c],[b,d],[c,d] ]
but it's not available for me

I also found:

http://permutation.rubyforge.org/\. I succeeded to install the gem,
but I couldn't accomplish the above.

So I've created my own method:

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
     puts newarr[0..14]
                 ==> [ [a,b],[a,c],[a,d],[b,c],[b,d],[c,d] ]

   end

end

//program

mm = ["a","b","c","d"]

mm.comby

//

It puts the right values, but what I can't use newarr ( tried also
@newarr)
in my program.

What would like to see:

mm = ["a","b","c","d"]
aa = mm.comby
puts aa
==> [ [a,b],[a,c],[a,d],[b,c],[b,d],[c,d] ]

What can I do??

Thanks!

4

Hi Ralf,

Thanx for pointing me towards this good collection called 'facets'.
But is there any difference in this case, just use some code..

···

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5

Well, if you really just need this one method, I think installing a
complete library is a bit too much. I mean, this is no special algorithm
but a very basic operation that you can program ad hoc.

···

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6

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

To advanced for newbie!! :slight_smile: Thnx for your help!

···

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7

I have no idea, how much your code is tested. But if you're new to ruby and you just need this functionality, why not use a well known library like facets? Of course you could do it yourself to avoid an external dependency. Unless this combination is a central thing in your application, I would let facets do the job and concentrate on the hard part the problem.

ralf

···

On 04/12/2012 03:41 PM, Ronnie Aa wrote:

Hi Ralf,

Thanx for pointing me towards this good collection called 'facets'.
But is there any difference in this case, just use some code..

8

Ok, I think you're right! I'm still new to ruby and programming ig,
so every piece of information is welcome..

···

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