code: public DBObject group(DBObject key, DBObject cond, DBObject initial, String reduce, String finalize)
              throws MongoException {
          GroupCommand cmd = new GroupCommand(dbCollection, key, cond, initial, reduce, finalize);
          return group(cmd);
      }
docs: Applies a group operation
  
  @param key      - { a : true }
  @param cond     - optional condition on query
  @param reduce   javascript reduce function
  @param initial  initial value for first match on a key
  @param finalize An optional function that can operate on the result(s) of the reduce function.
  @return The results
  @throws MongoException If an error occurred
  @see <a href="http://www.mongodb.org/display/DOCS/Aggregation">http://www.mongodb.org/display/DOCS/Aggregation</a>