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)```
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();
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);