def _point_mass(x, threshold=0.1):
    """
    Find point masses in pandas.Series with frequency exceeding
    specified value

    Parameters
    ----------

    x : pandas.Series

    threshold : float
        If value frequency exceeds threshold, consider value to have
        point mass

    Returns
    -------

    1-D numpy array that contains the point masses
    """
    cnts = x.value_counts(normalize=True)
    v = cnts[cnts > threshold].index.values
    v.sort()
    return v