def classify(enumrbl, &block)
      hash = {}
      enumrbl.each do |el|
        res = block.call el # tb res=yield(el)
        hash[res] = [] unless hash.has_key? res
        hash[res] << el
      end
      hash
    end
def classify(enumrbl, &block)
      hash = {}
      enumrbl.each do |el|
        res = block.call el # tb res=yield(el)
        hash[res] = [] unless hash.has_key? res
        hash[res] << el
      end
      hash
    end
Interessant iterador que classifica un enumerable
 (The Ruby Way , Ed. 2 - p 289)