public int getRequestId() {
        return parent.getGrouping().indexOf(this);
    }
Returns the id of this GroupingRequest.
This id is injected into the {@link RootGroup} of the final result, and
allows tracking of per-request meta data.

@return the id of this request, or -1 if it has been removed from the query select statement
container-search/src/main/java/com/yahoo/search/grouping/GroupingRequest.java