benchmarking some hash transformation techniques

hash_transform.out

Rehearsal -------------------------------------------------------
{}.tap                0.000382   0.000257   0.000639 (  0.000871)
[[]].to_h             0.000031   0.000001   0.000032 (  0.000032)
{}.each_with_object   0.000027   0.000001   0.000028 (  0.000028)
---------------------------------------------- total: 0.000699sec

                          user     system      total        real
{}.tap                0.000030   0.000001   0.000031 (  0.000029)
[[]].to_h             0.000033   0.000011   0.000044 (  0.000033)
{}.each_with_object   0.000023   0.000012   0.000035 (  0.000032)



Rehearsal -------------------------------------------------------
{}.tap                0.000264   0.000166   0.000430 (  0.000553)
[[]].to_h             0.000023   0.000001   0.000024 (  0.000023)
{}.each_with_object   0.000019   0.000000   0.000019 (  0.000020)
---------------------------------------------- total: 0.000473sec

                          user     system      total        real
{}.tap                0.000023   0.000002   0.000025 (  0.000024)
[[]].to_h             0.000029   0.000002   0.000031 (  0.000028)
{}.each_with_object   0.000032   0.000001   0.000033 (  0.000031)



Rehearsal -------------------------------------------------------
{}.tap                0.000301   0.000152   0.000453 (  0.000451)
[[]].to_h             0.000029   0.000001   0.000030 (  0.000029)
{}.each_with_object   0.000031   0.000007   0.000038 (  0.000037)
---------------------------------------------- total: 0.000521sec

                          user     system      total        real
{}.tap                0.000040   0.000001   0.000041 (  0.000039)
[[]].to_h             0.000027   0.000001   0.000028 (  0.000027)
{}.each_with_object   0.000025   0.000001   0.000026 (  0.000026)



Rehearsal -------------------------------------------------------
{}.tap                0.000252   0.000146   0.000398 (  0.000395)
[[]].to_h             0.000021   0.000001   0.000022 (  0.000020)
{}.each_with_object   0.000023   0.000004   0.000027 (  0.000026)
---------------------------------------------- total: 0.000447sec

                          user     system      total        real
{}.tap                0.000027   0.000002   0.000029 (  0.000026)
[[]].to_h             0.000025   0.000001   0.000026 (  0.000025)
{}.each_with_object   0.000024   0.000001   0.000025 (  0.000025)

hash_transform.rb

require "benchmark"
require "rspec"

1.times do
  Benchmark.bmbm do |x|
    include ::RSpec::Matchers

    keys = ("a".."z").to_a.map(&:to_sym)
    source_hash = keys.map do |key|
      subhash = keys.zip((1..26).to_a).map do |subkey, subval|
        [subkey, subval]
      end.to_h

      [key, subhash]
    end.to_h

    iterations = 1_000_000
    xform = 100

    x.report("{}.tap             ") do
      result = {}.tap do |h|
                 source_hash.each do |key, subhash|
                   h[key] = {
                     a: subhash[:a] * xform,
                     b: subhash[:b]
                   }
                 end
               end
      expect(result[:a][:a]).to eq xform
      expect(result[:b][:a]).to eq xform
      expect(result[:a][:b]).to eq 2
      expect(result[:b][:b]).to eq 2
    end

    x.report("[[]].to_h          ") do
      result = source_hash.map do |key, subhash|
                 [key, {a: subhash[:a] * xform, b: subhash[:b]}]
               end.to_h
      expect(result[:a][:a]).to eq xform
      expect(result[:b][:a]).to eq xform
      expect(result[:a][:b]).to eq 2
      expect(result[:b][:b]).to eq 2
    end

    x.report("{}.each_with_object") do
      result = source_hash.each_with_object({}) do |(key, subhash), newhash|
                 newhash[key] = {a: subhash[:a] * xform, b: subhash[:b]}
               end
      expect(result[:a][:a]).to eq xform
      expect(result[:b][:a]).to eq xform
      expect(result[:a][:b]).to eq 2
      expect(result[:b][:b]).to eq 2
    end
  end
end