https://twitter.com/mizchi/status/388194590076833792

hoges.rb

[1] pry(main)> hoges = 10.times.map{{fuga:10, piyo:20}}
=> [{:fuga=>10, :piyo=>20},
 {:fuga=>10, :piyo=>20},
 {:fuga=>10, :piyo=>20},
 {:fuga=>10, :piyo=>20},
 {:fuga=>10, :piyo=>20},
 {:fuga=>10, :piyo=>20},
 {:fuga=>10, :piyo=>20},
 {:fuga=>10, :piyo=>20},
 {:fuga=>10, :piyo=>20},
 {:fuga=>10, :piyo=>20}]
[2] pry(main)> hoges.map{|h|h[:fuga]}.reduce(&:+)
=> 100
[3] pry(main)> hoges.inject(0){|sum,hoge| sum+=hoge[:fuga]} 
=> 100
[4] pry(main)> fuga=Proc.new{|o| o[:fuga]}
=> #<Proc:0x007fd102876e98@(pry):1>
[5] pry(main)> hoges.map(&fuga).reduce(&:+)
=> 100