entropy: function [s][
    t: #[]
    loop s 'c [
        unless key? t c -> t\[c]: 0
        t\[c]: t\[c] + 1
    ]
    result: 0
    loop values t 'x ->
        'result - (x//(size s)) * log x//(size s) 2

    return result
]

print entropy "1223334444"