def METHOD_NAME(array_factory1, array_factory2):
    x = array_factory1([1, None, 3, 4])
    y = array_factory2([10, 20, 30, 40])
    df = vaex.from_arrays(x=x, y=y)
    df['y2'] = df.func.where(df.y > 20, None, df.x)
    assert df.y2.dtype == df.x.dtype
    assert df.y2.tolist() == [1, None, None, None]
    df['y3'] = df.func.where(df.y > 20, df.x, None)
    assert df.y3.dtype == df.x.dtype
    assert df.y3.tolist() == [None, None, 3, 4]