@Test
public void testGroup_Agg_Named() {

    DataFrame df1 = DataFrame.newFrame("a", "b").foldByRow(
            1, "x",
            2, "y",
            1, "y",
            0, "a",
            1, "x");
    DataFrame df = df1.group("b").agg(
            Aggregator.first("b"),
            Aggregator.sumLong("a").named("a_sum"),
            Aggregator.medianDouble("a").named("a_median"));
    new DataFrameAsserts(df, "b", "a_sum", "a_median")
            .expectHeight(3)
            .expectRow(0, "x", 2L, 1.)
            .expectRow(1, "y", 3L, 1.5)
            .expectRow(2, "a", 0L, 0.);
}