private final ImmutableMap<R, ImmutableMap<C, V>> rowMap;
  private final ImmutableMap<C, ImmutableMap<R, V>> columnMap;

  @SuppressWarnings("Immutable") // We don't modify this after construction.
  private final int[] rowCounts;

  @SuppressWarnings("Immutable") // We don't modify this after construction.
  private final int[] columnCounts;

  @SuppressWarnings("Immutable") // We don't modify this after construction.

  private final ImmutableMap<R, ImmutableMap<C, V>> rowMap;
  private final ImmutableMap<C, ImmutableMap<R, V>> columnMap;

  @SuppressWarnings("Immutable") // We don't modify this after construction.
  private final int[] rowCounts;

  @SuppressWarnings("Immutable") // We don't modify this after construction.
  private final int[] columnCounts;

  @SuppressWarnings("Immutable") // We don't modify this after construction.