have ruby, seek task

I really like Ruby. Working with it is just so much fun! I wrote my checkbook balancer in it, and everything else I do is pretty much just messing around because it’s fun. I need to find something more practical to do, but it’s usually easier for me to use Perl instead.

Today, I wondered how easy it would be to iterate over an array in n-sized chunks at a time. This came to mind because I want to iterate over pairs in a list in Rubric’s code. (I wish I’d written it in Ruby, sort of.)

So, I ended up writing a few methods for Array. It wasn’t hard, but I rewrote them a number of times, each time feeling like I was getting a better grip on the Ruby Way.

class Array
  def each_n(n, &block)
    (0 .. (self.size/n.to_f).ceil - 1).map { |i| block.call(self[i*n,n]) }
  end
  def collect_n(n, &block)
    c = []

    *each_n(n) { |nth| block.call(nth).each { |x| c << x } }

    return c
  end
  def collect_n!(n, &block)
    self[0, self.size] = self.collect_n(n, &block)
  end
  alias_method :map_n,  :collect_n
  alias_method :map_n!, :collect_n!
end

each_n iterates over the Array, invoking the passed block once for each n-sized chunk, which is passed as an Array. collect_n maps these chunks through the block. As Ruby standards suggest, collect_n! does the mapping and replaces the original list’s contents with the result.

What fun!

I don’t have personal application for this, so I had some pretty silly test/demo code:

digits = [ 1,2,3,4,5,6,7,8,9 ]

puts "digits counted in fives:"

*each_n(5) { |x| puts x, "---" }

puts "digits, multipled in threes by [0,1,2], counted in fives:"

*collect_n!(3) { |nth| i = -1; nth.map { |x| x * i+=1; } }
*each_n(5) { |x| puts x, "---" }

I should learn to use Ruby’s testing framework for this sort of thing!

Written on January 8, 2005