hash_max.rb

require 'benchmark'

N = 10000
HASH_SIZE = 10

HASH = {}
HASH_SIZE.times do |n|
  HASH[n] = (rand * 100).round - 50  
end
puts HASH.inspect

if RUBY_VERSION < '1.9'
  class Array
    def keys
      map(&:first)
    end
  end
end

Benchmark.bm(30) do |bm|
  bm.instance_exec do
    def test label
      report(label) {
        N.times {
          yield
        }
      }
    end
    def test19 label, &block
      if RUBY_VERSION > '1.9'
        test "#{label} (1.9)", &block
      end
    end

    test('max') { HASH.max { |a,b| a.last <=> b.last}.first }
    test('max (expanded)') { HASH.max { |(k1,v1),(k2,v2)| v1 <=> v2 }.first }
    test('max_by') { HASH.max_by(&:last).first }
    test('max_by (expanded)') { HASH.max_by { |k,v| v }.first }

    test('select') { HASH.select { |x,i| i == HASH.values.max }.keys }
    test('sort_by') { HASH.sort_by { |k,v| v }.last.first }
    test('invert') { HASH.invert[HASH.values.max] }
    if RUBY_VERSION > '1.9' # Hash#key was Hash#index in 1.8
      test('key') { HASH.key HASH.values.max }
    else
      test('key') { HASH.index HASH.values.max }
    end

    puts
    report('select (cache max)') do
      max = HASH.values.max
      N.times { HASH.select { |x,i| i == max }.keys }
    end
    report('invert (cache max)') do
      max = HASH.values.max
      N.times { HASH.invert[max] }
    end
    if RUBY_VERSION > '1.9'
      report('key (cache max)') do
        max = HASH.values.max
        N.times { HASH.key max }
      end
    else
      report('key (cache max)') do
        max = HASH.values.max
        N.times { HASH.index max }
      end
    end
  end
end

results 1.8

{5=>-13, 0=>-31, 6=>47, 1=>-47, 7=>-36, 2=>5, 8=>-32, 3=>-29, 9=>38, 4=>-21}
                                    user     system      total        real
max                             0.230000   0.000000   0.230000 (  0.228710)
max (expanded)                  0.240000   0.000000   0.240000 (  0.244368)
max_by                          0.250000   0.000000   0.250000 (  0.254624)
max_by (expanded)               0.160000   0.000000   0.160000 (  0.168497)
select                          0.810000   0.010000   0.820000 (  0.850495)
sort_by                         0.210000   0.000000   0.210000 (  0.215644)
invert                          0.110000   0.000000   0.110000 (  0.108169)
key                             0.060000   0.000000   0.060000 (  0.070295)

select (cache max)              0.210000   0.000000   0.210000 (  0.210509)
invert (cache max)              0.050000   0.000000   0.050000 (  0.048558)
key (cache max)                 0.010000   0.000000   0.010000 (  0.008889)

results 1.9

{0=>48, 1=>-48, 2=>1, 3=>-8, 4=>37, 5=>-23, 6=>-11, 7=>-37, 8=>3, 9=>13}
                                    user     system      total        real
max                             0.060000   0.000000   0.060000 (  0.051559)
max (expanded)                  0.040000   0.000000   0.040000 (  0.041429)
max_by                          0.040000   0.000000   0.040000 (  0.038113)
max_by (expanded)               0.040000   0.000000   0.040000 (  0.040344)
select                          0.260000   0.000000   0.260000 (  0.264688)
sort_by                         0.070000   0.000000   0.070000 (  0.070121)
invert                          0.070000   0.000000   0.070000 (  0.069767)
key                             0.030000   0.000000   0.030000 (  0.030712)

select (cache max)              0.030000   0.000000   0.030000 (  0.031417)
invert (cache max)              0.040000   0.010000   0.050000 (  0.038634)
key (cache max)                 0.000000   0.000000   0.000000 (  0.002110)