@Test
public void unique() {

  DoubleColumn uniq = DoubleColumn.create("test", 5, 4, 3, 2, 1, 5, 4, 3, 2, 1).unique();
  double[] arr = uniq.asDoubleArray();
  Arrays.sort(arr);
  assertArrayEquals(new double[] {1.0, 2.0, 3.0, 4.0, 5.0}, arr);
}