From: Brian Adkins <lojicdotcom@...>
Date: 2007-12-12T23:15:06+09:00
Subject: Re: Find the first non-nil element in an array

On Dec 11, 5:06 pm, Clifford Heath <n...@spam.please.net> wrote:
> I can't work out why you want to build a new (compacted) array in
> order to discard it and use the first element. Detect is much more
> suitable:

Depending on the nature of the array (in particular, the number of
initial nils), speed might be a reason to use compact instead of
detect. Although it seems counterintuitive, creating a new compacted
array just to grab the first element and throw it away can be faster
than using detect.

With the compact approach, there is one call to a method that is
compiled C code. With the detect approach, there are (possibly)
multiple iterations of interpreted Ruby.

I'd say compact is perfectly suitable for this purpose - it's more
concise, usually faster and logical.

require 'benchmark'
include Benchmark

ITER = 10000

def bench size, num_nils
  xs = Array.new(size, 'a')
  xs.fill(nil, 0, num_nils)

  bm(5) do |bench|
    bench.report('compact') do
      ITER.times { xs.compact[0] }
    end
    bench.report('detect') do
      ITER.times { xs.detect {|e| !e.nil? } }
    end
  end
end

[10,100,1000].each do |size|
  [0,1,9].each do |nils|
    bench(size, nils)
  end
end

--
Brian Adkins
http://www.lojic.com
http://lojic.com/blog/