Benchmarking shifting through an array versus calculating an offset when you need i to be i bet get at position i-1

shift-vs-offset.rb

require 'benchmark'

array_iterate = (1..10_000_000).to_a
array_shift   = array_iterate.dup

Benchmark.bmbm do |test|

  # this assumes you can destroy the given array
  test.report 'using shift' do
    for i in array_shift
      array_shift.shift
    end
  end

  test.report 'using an offset' do
    for i in array_iterate
      array_iterate[i-1]
    end
  end

end

MacRuby 0.9-nightly

Rehearsal ---------------------------------------------------
using shift       0.560000   0.000000   0.560000 (  0.561027)
using an offset   0.630000   0.010000   0.640000 (  0.654486)
------------------------------------------ total: 1.200000sec

                      user     system      total        real
using shift       0.280000   0.000000   0.280000 (  0.281825)
using an offset   0.630000   0.000000   0.630000 (  0.661343)