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

end

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

#@@@!leandro@mandigal:~!: ruby tmp/hash_from.rb
#             user     system      total        real
#leandro:  0.740000   0.000000   0.740000 (  0.745478)
#cassio :  0.500000   0.000000   0.500000 (  0.499253)
#caio   :  0.310000   0.000000   0.310000 (  0.314024)
#@@@!leandro@mandigal:~!: ruby tmp/hash_from.rb
#             user     system      total        real
#leandro:  0.750000   0.000000   0.750000 (  0.752957)
#cassio :  0.490000   0.000000   0.490000 (  0.499744)
#caio   :  0.310000   0.000000   0.310000 (  0.311485)
#@@@!leandro@mandigal:~!: ruby tmp/hash_from.rb
#             user     system      total        real
#leandro:  0.750000   0.000000   0.750000 (  0.754807)
#cassio :  0.500000   0.010000   0.510000 (  0.507627)
#caio   :  0.310000   0.000000   0.310000 (  0.316764)