条件を満たす要素をすべて見つける
a = [1,2,2,3,4,6,1,3,7,8,9] p a.delete_if {|x| (x % 2)==0 } #=> [1, 3, 1, 3, 7, 9] p a #=> [1, 3, 1, 3, 7, 9] a = [1,2,2,3,4,6,1,3,7,8,9] p a.find_all {|x| (x % 2)==0 } #=> [2, 2, 4, 6, 8] p a #=> [1, 2, 2, 3, 4, 6, 1, 3, 7, 8, 9] p %w[red green blue white black].grep(/\Ab/) #=> ["blue", "black"]