How to convert 2 dimensional array to Set?

Question

for the example I have Foo Object then I've some Foo Data inside 2-d Array Foo[][] . I want to convert it into Set<Foo> in order to just get Set of Foo unique data. How can I do that?

Answer 1

A simple (but not the best performing) solution would be to use java streams:

Set<Foo> set = Arrays.stream(array)
    .flatMap(Arrays::stream)
    .collect(Collectors.toSet());

The above code snippet first creates a Stream<Foo[]> with the Arrays.stream(array) statement.

Then it flattens that stream into Stream<Foo> with the second statement: .flatMap(Arrays::stream) which behaves the same as .flatMap(arr -> Arrays.stream(arr)) .

At last it creates a Set<Foo> out of the flattened stream with .collect(Collectors.toSet()) .

I suggest having a deep look at the Java Streaming API, introduced with Java 8. It can do much more than just mapping a 2d array into a Set.

---

Another approach is just to use 2 nested for loops:

Set<Foo> set = new HashSet<>(); // or LinkedHashSet if you need a similar order than the array
for(Foo[] inner : array) {
    for(Foo item : inner) {
        set.add(item);
    }
}

Answer 2

public <T> List<T> twoDArrayToList(T[][] twoDArray) {
    List<T> list = new ArrayList<T>();
    for (T[] array : twoDArray) {
        list.addAll(Arrays.asList(array));
    }
    return list;
}