>>> df = session.create_dataframe([[10, 11], [20, 22], [25, None], [30, 35]], schema=["v", "v2"])
>>> df.group_by("v").agg(regr_sxx(col("v"), col("v2")).alias("regr_sxx")).collect()
[Row(V=10, REGR_SXX=0.0), Row(V=20, REGR_SXX=0.0), Row(V=25, REGR_SXX=None), Row(V=30, REGR_SXX=0.0)]