From: Harry Kakueki <list.push@...>
Date: 2009-09-02T12:05:09+09:00
Subject: Re: Nice algorithm for 'spreading' indexes across an array?

On Wed, Sep 2, 2009 at 1:41 AM, Max Williams<toastkid.williams@gmail.com> wrote:
>
>>> arr = (1..12).to_a
> => [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12]
>
> I would get results back like this
>
> arr.spread(3)
> => [1,6,12] (or [1,7,12], either is fine)
>
> arr.spread(4)
> => [1, 5, 9, 12]  (or [1,4,8,12] or [1, 5, 8, 12])
>
> It feels like there should be a simple solution for this but i can't
> think of a nice way.  Anyone?
>
> thanks
> max
> --

I haven't tested enough to see if this always works.
But, take a look and make changes if necessary.


class Array
  def spread(num)
    res,de = [],[]
    (1..(size-num)).each{|u| de << size*u/(size-num+1)}
    (0...size).each{|y| res << self[y] if de.include?(y) == false}
    res
  end
end


arr = (1..12).to_a
(3..12).each{|t| p arr.spread(t)}

#output

#=> [1, 6, 12]
#=> [1, 4, 8, 12]
#=> [1, 3, 6, 9, 12]
#=> [1, 3, 5, 8, 10, 12]
#=> [1, 2, 4, 6, 8, 10, 12]
#=> [1, 2, 4, 6, 7, 9, 11, 12]
#=> [1, 2, 3, 5, 6, 8, 9, 11, 12]
#=> [1, 2, 3, 4, 6, 7, 8, 10, 11, 12]
#=> [1, 2, 3, 4, 5, 6, 8, 9, 10, 11, 12]
#=> [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12]



Harry

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