code: func (idx *Index) GroupByLimit(limit int64, rowsQueries ...*PQLRowsQuery) *PQLBaseQuery {
  	if len(rowsQueries) < 1 {
  		return NewPQLBaseQuery("", idx, errors.New("there should be at least one rows query"))
  	}
  	if limit < 0 {
  		return NewPQLBaseQuery("", idx, errors.New("limit must be non-negative"))
  	}
  	text := fmt.Sprintf("GroupBy(%s,limit=%d)", strings.Join(serializeGroupBy(rowsQueries...), ","), limit)
  	return NewPQLBaseQuery(text, idx, nil)
  }
docs: // GroupByLimit creates a GroupBy query with the given limit and Rows queries