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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:

def segment_radii(neurites, neurite_type=NeuriteType.all):
    '''arithmetic mean of the radii of the points in segments in a collection of neurites'''
    def _seg_radii(sec):
        '''vectorized mean radii'''
        pts = sec.points[:, COLS.R]
        return np.divide(np.add(pts[:-1], pts[1:]), 2.0)

    return map_segments(_seg_radii, neurites, neurite_type)