bm1.rb

require 'benchmark'

# [ 1, 2, 3, ..., 10_000 ]
array = (1..10000).to_a

# { 1=>1, 2=>2, ..., 10_000=>10_000 }
hash  = Hash[(0..9999).zip(1..10000)]

LOOPS = 1000

Benchmark.bm(10) do |bm|
  bm.report('array') do
    LOOPS.times do
      10_000.times {|i| array[i] }
    end
  end
  bm.report('hash') do
    LOOPS.times do
      10_000.times {|i| hash[i] }
    end
  end
end

bm1_results.txt

$ ruby -v
ruby 2.1.0p0 (2013-12-25 revision 44422) [x86_64-darwin11.0]
$ ruby bm1.rb 
                 user     system      total        real
array        1.060000   0.000000   1.060000 (  1.108306)
hash         1.920000   0.010000   1.930000 (  2.006488)

bm2.rb

require 'benchmark'

# [ 1, 2, 3, ..., 10_000 ]
array = (1..10000).to_a

# { 1=>1, 2=>2, ..., 10_000=>10_000 }
hash  = Hash[(1..10000).zip(1..10000)]

values = (1..10000).to_a

Benchmark.bm(10) do |bm|
  bm.report('array') do
    values.each do |val|
      array.index.each do |index|
        break if array[index] == val
      end
    end
  end
  bm.report('hash') do
    values.each do |val|
      hash.keys.each do |key|
        break if hash[key] == val
      end
    end
  end
end

bm2_results.txt

$ ruby bm2.rb 
                 user     system      total        real
array        6.090000   0.030000   6.120000 (  6.495695)
hash        11.850000   0.760000  12.610000 ( 13.343245)

bm3.rb

require 'benchmark'

array = (1..10000).map { rand(1_000_000) }
# odwrotny index
hash  = Hash[array.each_with_index.to_a.map(&:reverse)]

LOOPS = 10_000

Benchmark.bm(10) do |bm|
  bm.report('array') do
    LOOPS.times do
      array.find_index(rand(1_000_000))
    end
  end
  bm.report('hash') do
    LOOPS.times do
      hash[rand(1_000_000)]
    end
  end
end

bm3_results.txt

$ ruby bm3.rb 
                 user     system      total        real
array        0.670000   0.000000   0.670000 (  0.690233)
hash         0.010000   0.000000   0.010000 (  0.004873)