guava/src/com/google/common/collect/ArrayTable.java
@Override
  public Map<R, V> column(C columnKey) {
    checkNotNull(columnKey);
    Integer columnIndex = columnKeyToIndex.get(columnKey);
    return (columnIndex == null) ? ImmutableMap.<R, V>of() : new Column(columnIndex);
  }
@Override
  public Map<R, V> column(C columnKey) {
    checkNotNull(columnKey);
    Integer columnIndex = columnKeyToIndex.get(columnKey);
    return (columnIndex == null) ? ImmutableMap.<R, V>of() : new Column(columnIndex);
  }
Returns a view of all mappings that have the given column key. If the column key isn't in
{@link #columnKeySet()}, an empty immutable map is returned.

<p>Otherwise, for each row key in {@link #rowKeySet()}, the returned map associates the row key
with the corresponding value in the table. Changes to the returned map will update the
underlying table, and vice versa.

@param columnKey key of column to search for in the table
@return the corresponding map from row keys to values