hash_from.rb

require 'benchmark'

class Hash

  def hash_from_1(*keys)
    keys.inject({}) { |memo, obj| memo.merge(obj => self[obj]) }
  end

  def hash_from_2(*keys)
    self.dup.delete_if { |k, v| !keys.include? k }
  end

  def hash_from_3(*keys)
    Hash[keys.zip(self.values_at(*keys))]
  end

  def hash_from_4(*keys)
    hash = {}
    for k in keys
      hash[k] = self[k]
    end
    hash
  end

end

Benchmark.bm(7) do |b|
  hash = {:foo => 1, :bar => 2, :foobar => 3}

  b.report('leandro  :') { 100_000.times { hash.hash_from_1(:foo, :bar) } }
  b.report('cassio   :') { 100_000.times { hash.hash_from_2(:foo, :bar) } }
  b.report('caio     :') { 100_000.times { hash.hash_from_3(:foo, :bar) } }
  b.report('leandro-2:') { 100_000.times { hash.hash_from_4(:foo, :bar) } }
end

#@@@!leandro@mandigal:~!: ruby tmp/hash_from.rb
#             user     system      total        real
#leandro  :  0.750000   0.000000   0.750000 (  0.755851)
#cassio   :  0.500000   0.000000   0.500000 (  0.503797)
#caio     :  0.320000   0.000000   0.320000 (  0.316647)
#leandro-2:  0.260000   0.000000   0.260000 (  0.268218)
#@@@!leandro@mandigal:~!: ruby tmp/hash_from.rb
#             user     system      total        real
#leandro  :  0.750000   0.000000   0.750000 (  0.750898)
#cassio   :  0.500000   0.000000   0.500000 (  0.504918)
#caio     :  0.310000   0.000000   0.310000 (  0.315486)
#leandro-2:  0.270000   0.000000   0.270000 (  0.268886)
#@@@!leandro@mandigal:~!: ruby tmp/hash_from.rb
#             user     system      total        real
#leandro  :  0.750000   0.000000   0.750000 (  0.754943)
#cassio   :  0.500000   0.000000   0.500000 (  0.505592)
#caio     :  0.310000   0.000000   0.310000 (  0.314278)
#leandro-2:  0.270000   0.010000   0.280000 (  0.272884)