def get_nominal_integer_dict(nominal_vals):
    """
    Takes a set of nominal values (non-numeric)
    and returns a dictionary that maps each value
    to a unique integer
    """
    d = {}
    for val in nominal_vals:
        if val not in d:
            current_max = max(d.values()) if len(d) > 0 else -1
            d[val] = current_max + 1
    return d
