}

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

    @Override
    public Set<C> columnKeySet() {
      return fromTable.columnKeySet();
    }

    @Override
    Collection<V2> createValues() {
      return Collections2.transform(fromTable.values(), function);
    }

    @Override

    checkNotNull(columnKey, "columnKey");
    return MoreObjects.firstNonNull(
        (ImmutableMap<R, V>) columnMap().get(columnKey), ImmutableMap.<R, V>of());
  }

  @Override
  public ImmutableSet<C> columnKeySet() {
    return columnMap().keySet();
  }

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