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.
   */

  }

  public void testColumnSetPartialOverlap() {
    table = create("foo", 1, 'a', "bar", 1, 'b', "foo", 2, 'c', "bar", 3, 'd');
    assertThat(table.columnKeySet()).containsExactly(1, 2, 3);
  }

  @J2ktIncompatible
  @GwtIncompatible // NullPointerTester
  public void testNullPointerInstance() {

    assertEquals(ImmutableMap.of(), testTable.column(0));
    assertEquals(ImmutableMap.of('a', "blah"), testTable.column(1));
  }

  public void testColumnKeySet() {
    assertEquals(ImmutableSet.of(1), testTable.columnKeySet());
  }

  public void testColumnMap() {
    assertEquals(ImmutableMap.of(1, ImmutableMap.of('a', "blah")), testTable.columnMap());
  }

  public void testRow() {

import java.util.Map;

/**
 * Implementation of {@link Table} using linked hash tables. This guarantees predictable iteration
 * order of the various views.
 *
 * <p>The views returned by {@link #column}, {@link #columnKeySet()}, and {@link #columnMap()} have
 * iterators that don't support {@code remove()}. Otherwise, all optional operations are supported.
 * Null row keys, columns keys, and values are not supported.
 *

import java.util.Map;

/**
 * Implementation of {@link Table} using linked hash tables. This guarantees predictable iteration
 * order of the various views.
 *
 * <p>The views returned by {@link #column}, {@link #columnKeySet()}, and {@link #columnMap()} have
 * iterators that don't support {@code remove()}. Otherwise, all optional operations are supported.
 * Null row keys, columns keys, and values are not supported.
 *

    }
  }

  public void testColumnKeySet() {
    for (ImmutableTable<Character, Integer, String> testInstance : getTestInstances()) {
      assertEquals(ImmutableSet.of(1, 2), testInstance.columnKeySet());
    }
  }

  public void testColumnMap() {
    for (ImmutableTable<Character, Integer, String> testInstance : getTestInstances()) {
      assertEquals(
          ImmutableMap.of(

    return row.values().asList().get(columnIndex);
  }

  @Override
  @J2ktIncompatible
  @GwtIncompatible
    Object writeReplace() {
    Map<C, Integer> columnKeyToIndex = Maps.indexMap(columnKeySet());
    int[] cellColumnIndices = new int[cellSet().size()];
    int i = 0;
    for (Cell<R, C, V> cell : cellSet()) {
      // requireNonNull is safe because the cell exists in the table.

    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.
   */

 * returns a {@link SortedMap}, instead of the {@link Set} and {@link Map} specified by the {@link
 * Table} interface.
 *
 * <p>The views returned by {@link #column}, {@link #columnKeySet()}, and {@link #columnMap()} have
 * iterators that don't support {@code remove()}. Otherwise, all optional operations are supported.
 * Null row keys, columns keys, and values are not supported.
 *

 * returns a {@link SortedMap}, instead of the {@link Set} and {@link Map} specified by the {@link
 * Table} interface.
 *
 * <p>The views returned by {@link #column}, {@link #columnKeySet()}, and {@link #columnMap()} have
 * iterators that don't support {@code remove()}. Otherwise, all optional operations are supported.
 * Null row keys, columns keys, and values are not supported.
 *