class Hash
  def keys_matching(p, &block)
    s = {}
    
    self.each do |k,v|
      next unless k.match(p)
      
      v = yield(v, k) if block_given?
      
      s[k] = v
    end
    
    return s
  end
  
  def collect_values
    each do |k,v|
      self[k] = yield v
    end
  end
end