Benchmark building a Ruby hash: #each - #each_with_object - #reduce - Hash[map] - #map.zip(map).to_h - #reduce-merge

benchmark_building_a_hash.rb

require 'benchmark/ips'

Benchmark.ips do |x|

  Property = Struct.new(:name, :original_name)

  PROPERTIES = [
    Property.new("Clo",   "Chloe"     ),
    Property.new("Jon",   "Jonathan"  ),
    Property.new("Kris",  "Kristin"   ),
    Property.new("Dave",  "David"     ),
    Property.new("Ana",   "Anastasia" ),
    Property.new("Mike",  "Michael"   ),
    Property.new("Becky", "Rebecca"   ),
    Property.new("Will",  "William"   )
  ]

  x.report('#each') do |times|
    i = 0
    while i < times
      out = {}
      PROPERTIES.each do |property|
        out[property.name] = property.original_name
      end
      out
      i += 1
    end
  end
  
  x.report('#each_with_object') do |times|
    i = 0
    while i < times
      PROPERTIES.each_with_object({}) do |property, memo|
        memo[property.name] = property.original_name
      end
      i += 1
    end
  end

  x.report('#reduce') do |times|
    i = 0
    while i < times
      PROPERTIES.reduce({}) do |memo, property|
        memo[property.name] = property.original_name
        memo
      end
      i += 1
    end
  end

  x.report('Hash[map]') do |times|
    i = 0
    while i < times
      Hash[PROPERTIES.map { |property| [property.name, property.original_name] }]
      i += 1
    end
  end

  x.report('#map.zip(map).to_h') do |times|
    i = 0
    while i < times
      PROPERTIES.map(&:name).zip(PROPERTIES.map(&:original_name)).to_h
      i += 1
    end
  end

  x.report('#reduce-merge') do |times|
    i = 0
    while i < times
      PROPERTIES.reduce({}) { |memo, property| memo.merge(property.name => property.original_name) }
      i += 1
    end
  end

  x.compare!
end

Surprised to see that "Hash[map]" is by far the fastest on JRuby 9k.

Calculating -------------------------------------
               #each    20.365k i/100ms
   #each_with_object    19.043k i/100ms
             #reduce    16.627k i/100ms
           Hash[map]    22.174k i/100ms
  #map.zip(map).to_h    14.661k i/100ms
       #reduce-merge     7.936k i/100ms
-------------------------------------------------
               #each    302.582k (± 1.5%) i/s -      1.527M
   #each_with_object    288.721k (± 2.5%) i/s -      1.447M
             #reduce    236.231k (± 3.5%) i/s -      1.181M
           Hash[map]    352.435k (± 2.7%) i/s -      1.774M
  #map.zip(map).to_h    215.814k (± 2.4%) i/s -      1.085M
       #reduce-merge     98.931k (± 5.2%) i/s -    499.968k

Comparison:
           Hash[map]:   352435.2 i/s
               #each:   302582.0 i/s - 1.16x slower
   #each_with_object:   288721.1 i/s - 1.22x slower
             #reduce:   236231.1 i/s - 1.49x slower
  #map.zip(map).to_h:   215814.3 i/s - 1.63x slower
       #reduce-merge:    98931.2 i/s - 3.56x slower

irb(main):153:0> JRUBY_VERSION
=> "9.0.4.0"
irb(main):154:0> ^D
$ java -version
openjdk version "1.8.0_66-internal"
OpenJDK Runtime Environment (build 1.8.0_66-internal-b17)
OpenJDK 64-Bit Server VM (build 25.66-b17, mixed mode)

Thanks for the JRuby version! Interesting! That's cool for Hash[map] because it's my favorite version along with the zip FP-style pipeline. Also interesting that in JRuby reduce seems slower than each_with_object, whereas in MRI they are close and in MRI 2.3.0 they seem to be exactly the same.