Observations

  // test how file can be unfolded into multiple columns
  public void testUnfoldingColumn() throws IOException {
    // Here's the file
    File file = getFile("smalldata/chicago/chicagoAllWeather.csv");

    // Get all its lines
    final List<String> lines = Files.readLines(file, Charset.defaultCharset());

    // Store it in H2O, with typed column as a wrapper (core H2O storage is a type-unaware Vec class)
    Column<String> source = willDrop(Strings.newColumn(lines));

    // Produce another (virtual) column that stores a list of strings as a row value
    Column<List<String>> split = new UnfoldingColumn<>(Functions.splitBy(","), source, 10);

    // now check that we have the right data
    for (int i = 0; i < lines.size(); i++) {
      // Since we specified width (10), the rest of the list is filled with nulls; have to ignore them.
      // It's important to have the same width for the whole frame..
      String actual = StringUtils.join(" ", Predicate.NOT_NULL.filter(split.apply(i)));
      // So, have we lost any data?
      assertEquals(lines.get(i).replaceAll("\\,", " ").trim(), actual);
    }
  }