benchmark_hash_find.rb

require 'benchmark'
begin
  require 'active_support/values/time_zone'
rescue LoadError
  puts 'Please do `gem install active_support`'
  exit(1)
end

def benchmark_hash(hash, key, inverted_hash)
  Benchmark.bmbm do |x|
    x.report('finding in hash by value using select') do
      hash.select { |k, v| v == key }.keys.first
    end

    x.report('finding in hash by value using find') do
      hash.find { |k, v| v == key }.first
    end

    x.report('transposing & finding in hash by key') do
      hash.invert[key]
    end

    x.report('finding in hash by key using pre-inverted hash') do
      inverted_hash[key]
    end
  end
end

nums = 1..1000000
hash = nums.inject({}) do |memo, n|
  memo["key_#{n}"] = "value_#{n}"
  memo
end
printf "\e[1;31m Unrealistic dataset:\e[0m\n\n"
benchmark_hash(hash, "value_#{rand(nums.max)}", hash.invert)

printf "\n\e[1;31m Realistic dataset:\e[0m\n\n"
benchmark_hash(ActiveSupport::TimeZone::MAPPING, 'America/Chicago', hash.invert)

# ruby -e "$(curl -Ls http://git.io/8eHTIA)"

output.txt

 Unrealistic dataset:

Rehearsal ----------------------------------------------------------------------------------
finding in hash by value using select            0.360000   0.000000   0.360000 (  0.359564)
finding in hash by value using find              0.170000   0.010000   0.180000 (  0.178563)
transposing & finding in hash by key             1.900000   0.040000   1.940000 (  1.937345)
finding in hash by key using pre-inverted hash   0.000000   0.000000   0.000000 (  0.000004)
------------------------------------------------------------------------- total: 2.480000sec

                                                     user     system      total        real
finding in hash by value using select            0.350000   0.000000   0.350000 (  0.356475)
finding in hash by value using find              0.170000   0.000000   0.170000 (  0.163680)
transposing & finding in hash by key             1.730000   0.010000   1.740000 (  1.745643)
finding in hash by key using pre-inverted hash   0.000000   0.000000   0.000000 (  0.000007)

 Realistic dataset:

Rehearsal ----------------------------------------------------------------------------------
finding in hash by value using select            0.000000   0.000000   0.000000 (  0.000029)
finding in hash by value using find              0.000000   0.000000   0.000000 (  0.000007)
transposing & finding in hash by key             0.000000   0.000000   0.000000 (  0.000048)
finding in hash by key using pre-inverted hash   0.000000   0.000000   0.000000 (  0.000003)
------------------------------------------------------------------------- total: 0.000000sec

                                                     user     system      total        real
finding in hash by value using select            0.000000   0.000000   0.000000 (  0.000034)
finding in hash by value using find              0.000000   0.000000   0.000000 (  0.000014)
transposing & finding in hash by key             0.000000   0.000000   0.000000 (  0.000062)
finding in hash by key using pre-inverted hash   0.000000   0.000000   0.000000 (  0.000006)

Cool way to find the truth! Maybe you can give a talk on those cool ruby features some day!