reject和reject!
reject返回不滿足程式碼塊的元素陣列
reject！刪除陣列中滿足程式碼塊的元素

a=[1,2,3,5]
a.reject! {|x| x<4}
p a #[5]

b = [1,2,3,4,5]
c = b.reject {|x| x>4}
p c
p b

[1, 2, 3, 4]
[1, 2, 3, 4, 5]