speech-maturity-tests/votes_distrib.stan

functions {
    real model_lpmf(array[] int counts,
        int start, int end,
        array[,] int votes,
        vector alphas
        ) {
            real ll = 0;
            for (k in start:end) {
                ll += dirichlet_multinomial_lpmf(votes[k] | alphas);
            }
            return ll;
        }
}

data {
    int<lower=1> N;
    int<lower=1> C;
    array[N,C] int<lower=0> votes;
}

transformed data {
    array[N] int counts;
    for (i in 1:N) {
        counts[i] = sum(votes[i]);
    }
}

parameters {
    vector<lower=0>[C] alphas;
    //array[N] simplex[C] p;
}

model {
    target += reduce_sum(
      model_lpmf, counts, 1,
      votes, alphas
    );

    alphas ~ exponential(1);
}

generated quantities {
    simplex[C] p = dirichlet_rng(alphas);
}