Remove duplicates from a list of objects based multiple attributes in Java 8

Question

I want to compare getCode & getMode and find duplicate records.

Then there is one more product attribute getVode which always has different value(either true or false) in both records.

P1   getCode  getMode  getVode
1    001      123      true
P2   getCode  getMode  getVode
2    001      123      false

I tried below but it only finds duplicates:

List<ProductModel> uniqueProducts = productsList.stream()
    .collect(Collectors.collectingAndThen(
        toCollection(() -> new TreeSet<>(
            Comparator.comparing(ProductModel::getCode)
                .thenComparing(ProductModel::getMode)
        )),
        ArrayList::new));

So when I find duplicates records, I want to check the getVode value which is false and remove it from list. Any help would be appreciated?

Answer 1

As far as I understood, you want to remove elements only if they are a duplicate and their getVode method returns false.

We can do this literally. First, we have to identify which elements are duplicates:

Map<Object, Boolean> isDuplicate = productsList.stream()
    .collect(Collectors.toMap(pm -> Arrays.asList(pm.getCode(), pm.getMode()),
                              pm -> false, (a, b) -> true));

Then, remove those fulfilling the condition:

productsList.removeIf(pm -> !pm.getVode()
                         && isDuplicate.get(Arrays.asList(pm.getCode(), pm.getMode())));

Or, not modifying the old list:

List<ProductModel> uniqueProducts = new ArrayList<>(productsList);
uniqueProducts.removeIf(pm -> !pm.getVode()
                           && isDuplicate.get(Arrays.asList(pm.getCode(), pm.getMode())));

which can also be done via Stream operation:

List<ProductModel> uniqueProducts = productsList.stream()
    .filter(pm -> pm.getVode()
              || !isDuplicate.get(Arrays.asList(pm.getCode(), pm.getMode())))
    .collect(Collectors.toList());