Jer on Rails

Jay Fields: Array#chunk

• Posted September 11th, 2007 by Jeremy Weiskotten.
• 2 comments

Jay Fields of ThoughtWorks posted an interesting problem: break an Array up into a given number of “chunks”. He provides an example implementation and unit tests that define the expected behavior.

I posted my solution in a comment, but here it is again (I really need to figure out how to get syntax coloring…):

class Array  def chunk(number_of_chunks)    chunks = (1..number_of_chunks).collect { [] }    self.each_with_index do |item, index|      chunks[index % number_of_chunks] << item    end    chunks  end

  alias / chunkend

My solution is a little different than his. First, mine doesn’t modify the contents of the Array; his does. Since his does, the method should really be named “chunk!”, that exclamation point being the convention that indicates that it mutates the instance on which it is called. The unit tests don’t enforce one or the other, so I decided to follow convention.

Second, I’ve got one loop, which is over the Array being chunked. He’s got a nested loop, which I think increases the complexity quite a bit.

There’s a little bit of cleverness in my solution. I figure out which chunk to add the item to using the % modulus operator. This may not be a very common idiom, but it works and you don’t need a separate counter with boundary testing to cycle back to zero.