Radix Sort in Ruby

Radix.rb

def radix (a, base = 10) 
    m = a.max
    exp = 1 
    loop do
        bkt = Array.new(base){[]}
        a.each{|elem|
            pos = (elem / exp) % base
            bkt[pos] << elem
        }   
        a = bkt.flatten
        exp *= base
        break if exp > m 
    end 
    a   
end