* iterators that don't support {@code remove()}. Otherwise, all optional operations are supported.
 * Null row keys, columns keys, and values are not supported.
 *
 * <p>Lookups by row key are often faster than lookups by column key, because the data is stored in
 * a {@code Map<R, Map<C, V>>}. A method call like {@code column(columnKey).get(rowKey)} still runs

   * Returns an iterator containing the elements of {@code array} in order. The returned iterator is
   * a view of the array; subsequent changes to the array will be reflected in the iterator.
   *
   * <p><b>Note:</b> It is often preferable to represent your data using a collection type, for
   * example using {@link Arrays#asList(Object[])}, making this method unnecessary.
   *