assertEquals(data.getValue("A"), new Double(2.0));
        assertEquals(data.getValue("B"), null);
        assertEquals(data.getValue("C"), new Double(1.0));
        assertEquals(data.getValue("D"), new Double(3.0));

        // check retrieve value by index
        assertEquals(data.getValue(0), new Double(3.0));
        assertEquals(data.getValue(1), new Double(1.0));