http://stackoverflow.com/questions/6433177/performance-iterate-over-an-array-except-for-an-element

bench.rb

require 'benchmark'

array = [*(1..9)] * 1_000_000

Benchmark.bmbm do |bm|
  bm.report "with if" do
    array.each_with_index do |element, i|
      next if i == 1
      element - 1
    end
  end

  bm.report "without if" do
    array.each do |element|
      element - 1
    end
  end

  bm.report "with reject" do
    array.each_with_index.reject {|el,i| i == 1}.each do |el, i|
      el- 1
    end
  end

  bm.report "with first and drop" do
    n = 1
    (array.first(n) + array.drop(n + 1)).each do |el|
      el- 1
    end
  end

  bm.report "with ranges" do
    n = 1
    ((0...n).to_a + ((n+1)...array.size).to_a).map{|i| array[i]}.each do |el|
      el - 1
    end
  end
end

gistfile1.txt

→ ruby -v bench.rb                                                                                                                                                          
ruby 1.9.2p180 (2011-02-18 revision 30909) [x86_64-darwin10.6.0]
Rehearsal -------------------------------------------------------
with if               1.830000   0.010000   1.840000 (  1.847044)
without if            1.230000   0.000000   1.230000 (  1.244233)
with reject           5.730000   1.720000   7.450000 ( 11.672952)
with first and drop   1.290000   0.060000   1.350000 (  1.694164)
with ranges           3.880000   0.390000   4.270000 (  4.543618)
--------------------------------------------- total: 16.140000sec

                          user     system      total        real
with if               1.830000   0.000000   1.830000 (  1.832242)
without if            1.230000   0.000000   1.230000 (  1.239936)
with reject           5.040000   0.340000   5.380000 (  5.428142)
with first and drop   1.270000   0.010000   1.280000 (  1.292207)
with ranges           3.580000   0.190000   3.770000 (  3.802674)