code: def test_negative_index() -> None:
      df = pl.DataFrame({"a": [1, 2, 3, 4, 5, 6]})
      assert df.select(pl.col("a").gather([0, -1])).to_dict(
          as_series=False
      ) == {"a": [1, 6]}
      assert df.group_by(pl.col("a") % 2).agg(
          b=pl.col("a").gather([0, -1])
      ).sort("a").to_dict(as_series=False) == {
          "a": [0, 1],
          "b": [[2, 6], [1, 5]],
      }
  
label_desc: Use image node_id 1 for calling a global function with example usage: test_negative_index() without return types