def cal_support(freq, n_rows):
    """
    Calculate support

    Parameters
    ----------
    freq : int
        frequation of data.
            for example :
                32
    n_rows : int
        rows of data.
            for example :
                100

    Returns
    -------
    support.
        for example :
            = 32 / 100
            = 0.32


    """

    if n_rows == 0:
        raise ValueError("The rows supposed not to be zero")

    support = freq / n_rows

    return round(support, 3)