Distinct value from ArrayList in JAVA

Question

I have the following ArrayLists: 1) List<MAP<String,String>> in 2) ArrayList<>() :

[
[{name=a,age=33,city=NY},{name=b,age=23,city=NY},{name=d,age=83,city=CA}],
[{name=f,age=53,city=FL}],
[{name=d,age=11,city=TX},{name=a,age=13,city=CA}],
]

I want to get new ArrayList with distinct values of names as:

[{a},{b},{d},{f}]

Can you assist :)?

Answer 1

You can Iterate through your collection and add it to a Hash set to get Unique names.

List<Map<String,String>> input = new ArrayList<>();
    Set <String> uniqueNames = new HashSet<>();
    for( Map<String, String> stringStringMap : input )
        uniqueNames.add(stringStringMap.get("name"));

Or In Java8 this can be done in one line using stream

  Set<String> uniqueNames = input.stream().map(a -> a.get("name")).collect(Collectors.toSet());

And then you can use set to create an ArrayList(as you mentioned ArrayList in question ).

Answer 2

Using Java 8 you can do

//List<Map<String, String>> inList = new ArrayList<>(); 

List<String> outList = inList.stream().map(m -> m.get("name")).distinct().collect(Collectors.toList());