so-9538090-bm.rb

# Benchmarking for http://stackoverflow.com/questions/9538090

require 'benchmark'
require 'active_support/core_ext'

events = [{id:2, start:"3:30",break:30,num_attendees:14},{id:3, start:"3:40",break: 40,num_attendees:4},{id:4, start:"4:40",break:10,num_attendees:40}]

time = Benchmark.bm(10) do |bm|
  bm.report("amarshall 1") do
    10000.times do
      events.map do |hash|
        hash.select do |key, value|
          [:id, :start].include? key
        end
      end
    end
  end

  bm.report("amarshall 2") do
    10000.times do
      events.map do |hash|
        { id: hash[:id], start: hash[:start] }
      end
    end
  end

  bm.report("amarshall 3") do
    10000.times do
      return_keys = [:id, :start]
      events.map do |hash|
        {}.tap do |new_hash|
          return_keys.each do |key|
            new_hash[key] = hash[key]
          end
        end
      end
    end
  end

  bm.report("tadman 1") do
    10000.times do
      return_keys = [ :id, :start ]

      # Compute a quick hash to extract the right values: { key => true }
      key_index = Hash[return_keys.collect { |key| [ key, true ] }]

      return_array = events.collect do |event|
        event.select do |key, value|
          key_index[key]
        end
      end
    end
  end

  bm.report("tadman 2") do
    10000.times do
      return_keys = [ :id, :start ]

      return_array = events.collect do |event|
        Hash[
          return_keys.collect do |key|
            [ key, event[key] ]
          end
        ]
      end
    end
  end

  bm.report("mu") do
    10000.times do
      return_array = events.map { |h| h.slice(:id, :start) }
    end
  end
end