RosettaCodeData/Task/Entropy/Aime/entropy.aime

integer c;
real h, v;
index x;
data s;

for (, c in (s = argv(1))) {
    x[c] += 1r;
}

h = 0;
for (, v in x) {
    v /= ~s;
    h -= v * log2(v);
}

o_form("/d6/\n", h);