return cellRowIndices.length;
  }

  @Override
  Cell<R, C, V> getCell(int index) {
    int rowIndex = cellRowIndices[index];
    int columnIndex = cellColumnIndices[index];
    R rowKey = rowKeySet().asList().get(rowIndex);
    C columnKey = columnKeySet().asList().get(columnIndex);
    // requireNonNull is safe because we use indexes that were populated by the constructor.

  /**
   * Returns a set of row keys that have one or more values in the table. Changes to the set will
   * update the underlying table, and vice versa.
   *
   * @return set of row keys
   */
  Set<R> rowKeySet();

  /**
   * Returns a set of column keys that have one or more values in the table. Changes to the set will
   * update the underlying table, and vice versa.
   *
   * @return set of column keys
   */

    checkNotNull(rowKey, "rowKey");
    return MoreObjects.firstNonNull((ImmutableMap<C, V>) rowMap().get(rowKey), ImmutableMap.of());
  }

  @Override
  public ImmutableSet<R> rowKeySet() {
    return rowMap().keySet();
  }

  /**
   * {@inheritDoc}
   *
   * <p>The value {@code Map<C, V>} instances in the returned map are {@link ImmutableMap} instances
   * as well.
   */

    checkNotNull(rowKey, "rowKey");
    return MoreObjects.firstNonNull((ImmutableMap<C, V>) rowMap().get(rowKey), ImmutableMap.of());
  }

  @Override
  public ImmutableSet<R> rowKeySet() {
    return rowMap().keySet();
  }

  /**
   * {@inheritDoc}
   *
   * <p>The value {@code Map<C, V>} instances in the returned map are {@link ImmutableMap} instances
   * as well.
   */

  /**
   * Returns a set of row keys that have one or more values in the table. Changes to the set will
   * update the underlying table, and vice versa.
   *
   * @return set of row keys
   */
  Set<R> rowKeySet();

  /**
   * Returns a set of column keys that have one or more values in the table. Changes to the set will
   * update the underlying table, and vice versa.
   *
   * @return set of column keys
   */

    assertThat(sortedTable.rowKeySet().first()).isEqualTo("bar");
  }

  public void testRowKeySetLast() {
    sortedTable = create("foo", 1, 'a', "bar", 1, 'b', "foo", 3, 'c');
    assertThat(sortedTable.rowKeySet().last()).isEqualTo("foo");
  }

  public void testRowKeySetHeadSet() {
    sortedTable = create("foo", 1, 'a', "bar", 1, 'b', "foo", 3, 'c');
    Set<String> set = sortedTable.rowKeySet().headSet("cat");

      synchronized (mutex) {
        return set(delegate().cellSet(), mutex);
      }
    }

    @Override
    public Set<R> rowKeySet() {
      synchronized (mutex) {
        return set(delegate().rowKeySet(), mutex);
      }
    }

    @Override
    public Set<C> columnKeySet() {
      synchronized (mutex) {
        return set(delegate().columnKeySet(), mutex);

      synchronized (mutex) {
        return set(delegate().cellSet(), mutex);
      }
    }

    @Override
    public Set<R> rowKeySet() {
      synchronized (mutex) {
        return set(delegate().rowKeySet(), mutex);
      }
    }

    @Override
    public Set<C> columnKeySet() {
      synchronized (mutex) {
        return set(delegate().columnKeySet(), mutex);

      @Override
      public boolean retainAll(Collection<?> c) {
        return removeFromColumnIf(Maps.valuePredicateOnEntries(not(in(c))));
      }
    }
  }

  @Override
  public Set<R> rowKeySet() {
    return rowMap().keySet();
  }

  @LazyInit private transient @Nullable Set<C> columnKeySet;

  /**
   * {@inheritDoc}
   *

      @Override
      public boolean retainAll(Collection<?> c) {
        return removeFromColumnIf(Maps.valuePredicateOnEntries(not(in(c))));
      }
    }
  }

  @Override
  public Set<R> rowKeySet() {
    return rowMap().keySet();
  }

  @LazyInit private transient @Nullable Set<C> columnKeySet;

  /**
   * {@inheritDoc}
   *