code: func (f *Field) TopN(n uint64) *PQLRowQuery {
  	q := NewPQLRowQuery(fmt.Sprintf("TopN(%s,n=%d)", f.name, n), f.index, nil)
  	return q
  }
docs: // TopN creates a TopN query with the given item count.
  // Returns the id and count of the top n rows (by count of columns) in the field.