From: David Alan Black <dblack@...>
Date: 2000-12-18T08:37:22+09:00
Subject: [ruby-talk:7521] Re: flatten_by(n)

On Mon, 18 Dec 2000, David Alan Black wrote:

> On Mon, 18 Dec 2000, David Alan Black wrote:
>
> Next iteration:
> 
>   def flatten_once
>     res = []
>     for e in self
>       res.push e if e.nil?
>       res += e.to_a
>     end
>     res
>   end
> 

I don't know about the rest of you, but I've learned a lot today about
how arrays get extended in Ruby :-)

The above breaks on empty strings.  "".to_a => [], and
[1,2,3] + [] == [1,2,3].  So if you have "" in the original
array, it will disappear.

So -- I'm actually back to something quite similar to Ben's
first suggestion, in response to my recursive version, except
I'm using concat instead of '+=' because concat is a lot faster.
(Surprisingly faster, to me.)

  def flatten_once
    res = []
    for e in self
      if e.is_a? Array then res.concat e else res.push e end
    end
    res
  end


For the record:

30000 iterations:

      user     system      total        real
 10.330000   0.000000  10.330000 ( 10.327764)  # res.concat ...
 13.490000   0.000000  13.490000 ( 13.506367)  # res += ...

And now I really must go do some real work....


David

-- 
David Alan Black
home: dblack@candle.superlink.net
work: blackdav@shu.edu
Web:  http://pirate.shu.edu/~blackdav