code: public AggregateOperator<T> aggregate(Aggregations agg, int field) {
  		return new AggregateOperator<T>(this, agg, field);
  	}
docs: Applies an Aggregate transformation on a grouped {@link Tuple} {@link DataSet}.<br/>
  <b>Note: Only Tuple DataSets can be aggregated.</b>
  The transformation applies a built-in {@link Aggregations Aggregation} on a specified field
  of a Tuple group. Additional aggregation functions can be added to the resulting
  {@link AggregateOperator} by calling {@link AggregateOperator#and(Aggregations, int)}.
  
  @param agg The built-in aggregation function that is computed.
  @param field The index of the Tuple field on which the aggregation function is applied.
  @return An AggregateOperator that represents the aggregated DataSet.
  
  @see Tuple
  @see Aggregations
  @see AggregateOperator
  @see DataSet