javajava-8java-12

Filter list of custom object by specific object field


I have an object Batch (String id, Instant date, Long version)

I have a list of Batch and I want to filter to keep one batch for each id where version is the highest i.e:

batch1 = Batch(1, date, 5)
batch2 = Batch(2, date, 4)
batch3 = Batch(2, date, 7)
batch4 = Batch(1, date, 2)
batch5 = Batch(1, date, 4)
batch6 = Batch(3, date, 2)

after filtering I need to have 
List.of(batch1, batch3, batch6)```

Solution

  • You can use stream with toMap like this:

    Collection<Batch> highestVersionBatches = batches.stream()
            .collect(Collectors.toMap(
                    Batch::getId,
                    batch -> batch,
                    (e, r) -> e.getVersion() >= r.getVersion() ? e : r //<-- magic is here
            )).values();
    
    Outputs
    Batch(1, 2023-11-07, 5)
    Batch(2, 2023-11-07, 7)
    Batch(3, 2023-11-07, 2)
    

    If you want to get List instead of Collection, you can simply use:

    List<Batch> result = new ArrayList<>(highestVersionBatches);