public <RES extends Map<K, Group>> ResultTransformer<RES> as(Supplier<RES> mapFactory, Expression<?>... expressions) {
        return new GroupByGenericMap<K, Group, RES>(mapFactory, key, expressions);
    }
Get the results as a map

@param mapFactory the map factory to use, i.e. {@code HashMap::new}.
@param expressions projection
@return new result transformer
querydsl-core/src/main/java/com/querydsl/core/group/GroupByBuilder.java