code: public static <K, V> HashBagMultimap<V, K> flip(ListMultimap<K, V> listMultimap)
      {
          final HashBagMultimap<V, K> result = new HashBagMultimap<V, K>();
          listMultimap.forEachKeyMultiValues(new Procedure2<K, Iterable<V>>()
          {
              public void value(final K key, Iterable<V> values)
              {
                  Iterate.forEach(values, new Procedure<V>()
                  {
                      public void value(V value)
                      {
                          result.put(value, key);
                      }
                  });
              }
          });
          return result;
      }
docs: Flip the keys and values of the multimap.