Filter objects from a list that have the same member

Question

I have a list of objects. The object looks like this:

public class Slots {
  String slotType;
  Visits visit;
}


public class Visits {
  private long visitCode;
  private String agendaCode;
  private String scheduledTime;
  private String resourceType;
  private String resourceDescription;
  private String visitTypeCode;
  ...
}

I need to find the elements that have the same agendaCode, visitTypeCode and scheduledTime and for the life of me I can't get it done.

I tried this:

Set<String> agendas = slotsResponse.getContent().stream()
    .map(Slots::getVisit)
    .map(Visits::getAgendaCode)
    .collect(Collectors.toUnmodifiableSet());

Set<String> visitTypeCode = slotsResponse.getContent().stream()
    .map(Slots::getVisit)
    .map(Visits::getVisitTypeCode)
    .collect(Collectors.toUnmodifiableSet());

Set<String> scheduledTime = slotsResponse.getContent().stream()
    .map(Slots::getVisit)
    .map(Visits::getScheduledTime)
    .collect(Collectors.toUnmodifiableSet());

List<Slots> collect = slotsResponse.getContent().stream()
    .filter(c -> agendas.contains(c.getVisit().getAgendaCode()))
    .filter(c -> visitTypeCode.contains(c.getVisit().getVisitTypeCode()))
    .filter(c -> scheduledTime.contains(c.getVisit().getScheduledTime()))
    .collect(Collectors.toList());

But it's not doing what I thought it would. Ideally I would have a list of lists, where each sublist is a list of Slots objects that share the same agendaCode, visitTypeCode and scheduledTime. I struggle with functional programming so any help or pointers would be great!

This is Java 11 and I'm also using vavr.

Answer 1

Since you mentioned you're using vavr, here is the vavr way to solve this question.

Supposed you have your io.vavr.collection.List (or Array or Vector or Stream or similar vavr collection) of visits:

List<Visits> visits = ...;

final Map<Tuple3<String, String, String>, List<Visits>> grouped =
    visits.groupBy(visit ->
        Tuple.of(
            visit.getAgendaCode(),
            visit.getVisitTypeCode(),
            visit.getScheduledTime()
        )
    );

Or with a java.util.List of visits:

List<Visits> visits = ...;

Map<Tuple3<String, String, String>, List<Visits>> grouped = visits.stream().collect(
    Collectors.groupingBy(
        visit ->
            Tuple.of(
                visit.getAgendaCode(),
                visit.getVisitTypeCode(),
                visit.getScheduledTime()
            )
    )
);

Answer 2

The easiest way is to define a new class with necessaries fields (agendaCode, visitTypeCode and scheduledTime). Don't forget about equals/hashcode.

public class Visits {
    private long visitCode;
    private String resourceType;
    private String resourceDescription;
    private Code code;
    ...
}
class Code {
    private String agendaCode;
    private String scheduledTime;
    private String visitTypeCode;
    ...
    @Override
    public boolean equals(Object o) {...}
    @Override
    public int hashCode() {...}
}

Then you can use groupingBy like:

Map<Code, List<Slots>> map = slotsResponse.getContent().stream()
            .collect(Collectors.groupingBy(s -> s.getVisit().getCode()));

Also you can just implement equals method inside Visits only for agendaCode, visitTypeCode and scheduledTime. In this case use groupingBy by s.getVisit()