@Test
void asDoubleArray() {

  String[] words = {"foo", "bar", "larry", "foo", "lion", null, "ben", "tiger", "bar"};
  StringColumn wordColumn = StringColumn.create("words", words);
  double[] result = wordColumn.asDoubleArray();
  assertArrayEquals(
      new double[] {0.0, 1.0, 2.0, 0.0, 3.0, 4.0, 5.0, 6.0, 1.0}, result, 0.000_000_1);
}