def fit_cluster(data, assignments, k, P_init, R_init, means):
    """
    Fits NB/poisson params to a cluster.
    """
    for c in range(k):
        if data[:,assignments==c].shape[1] == 0:
            _, assignments = kmeans_pp(data, k)
    genes, cells = data.shape
    nb_gene_indices = np.array([True for i in range(genes)])
    for c in range(k):
        c_data = data[:,assignments==c]
        nb_gene_indices = nb_gene_indices & find_nb_genes(c_data)
    for c in range(k):
        c_data = data[:,assignments==c]
        nb_genes = c_data[nb_gene_indices,:]
        poisson_genes = c_data[~nb_gene_indices, :]
        P_init[nb_gene_indices, c], R_init[nb_gene_indices, c] = nb_fit(nb_genes)
        means[~nb_gene_indices, c] = poisson_genes.mean(1)
    return nb_gene_indices
Fits NB/poisson params to a cluster.