def calc_std(c0, c1=[]):
    """ Calculates the variance of the data."""
    if c1 == []:
        return numpy.std(c0, 0)
    prop = float(len(c0)) / float(len(c1))
    if prop < 1:
        p0 = int(math.ceil(1 / prop))
        p1 = 1
    else:
        p0 = 1
        p1 = int(math.ceil(prop))
    return numpy.std(numpy.vstack(p0 * [c0] + p1 * [c1]), 0)
Calculates the variance of the data.