Converting a list of object values to group

StonecoldIM :

I have the following piece of code

OrderCriteria o1 = new OrderCriteria(1, 1, 101, 201);
OrderCriteria o2 = new OrderCriteria(1, 1, 102, 202);
OrderCriteria o4 = new OrderCriteria(1, 1, 102, 201);
OrderCriteria o5 = new OrderCriteria(2, 2, 501, 601);
OrderCriteria o6 = new OrderCriteria(2, 2, 501, 602);
OrderCriteria o7 = new OrderCriteria(2, 2, 502, 601);
OrderCriteria o8 = new OrderCriteria(2, 2, 502, 602);
OrderCriteria o9 = new OrderCriteria(2, 2, 503, 603);

Where OrderCriteria looks like below:

public class OrderCriteria {
    private final long orderId;
    private final long orderCatalogId;
    private final long procedureId;
    private final long diagnosisId;

    public OrderCriteria(long orderId, long orderCatalogId, long procedureId, long diagnosisId) {
        this.orderId = orderId;
        this.orderCatalogId = orderCatalogId;
        this.procedureId = procedureId;
        this.diagnosisId = diagnosisId;
    }

    // Getters
}

What I want is to get a list of procedures and list of diagnosis grouped by order id. So it should return:

{1, {101, 102}, {201, 202}}
{2, {501, 502, 503}, {601, 602, 603}}

which means Order with id 1 is having procedure ids 101, 102 and diagnosis ids 201, 202 etc. I tried using google guava table but could not come up with any valid solution.

shmosel :

First you'll need a new structure to hold the grouped data:

class OrderCriteriaGroup {
    final Set<Long> procedures = new HashSet<>();
    final Set<Long> diagnoses = new HashSet<>();

    void add(OrderCriteria o) {
        procedures.add(o.getProcedureId());
        diagnoses.add(o.getDiagnosisId());
    }

    OrderCriteriaGroup merge(OrderCriteriaGroup g) {
        procedures.addAll(g.procedures);
        diagnoses.addAll(g.diagnoses);
        return this;
    }
}

add() and merge() are convenience methods that will help us stream and collect the data, like so:

Map<Long, OrderCriteriaGroup> grouped = criteriaList.stream()
        .collect(Collectors.groupingBy(OrderCriteria::getOrderId,
                Collector.of(
                        OrderCriteriaGroup::new,
                        OrderCriteriaGroup::add,
                        OrderCriteriaGroup::merge)));