def _probability(value, col_a_counts_map):
    """ p(a=value) = counts of a at value, dividied by total values of a """    
    sum=0
    for key in col_a_counts_map.keys():
        sum += col_a_counts_map[key]

    if  col_a_counts_map[value] == 0:
        print("nothing:", value)
    return col_a_counts_map[value] / float(sum)