distinct with key selector

[zhuker]

ala http://reactivex.io/RxJava/1.x/javadoc/rx/Observable.html#distinct-rx.functions.Func1-

stream = Stream.of("a1", "b1", "c2", "c3");
distinct = StreamUtils.distinct(stream, str -> str.charAt(1));
distinct.forEach(x -> System.out.println(x));

prints:

a1
c2
c3

[JosePaumard]

Thank you for your comment, seems like a very good idea, and not too hard to implement. If the stream is ordered, I see the behavior of this operator, but what should it be for non-ordered streams? That is if the stream you give as an example is equivalent to this one:

stream = Stream.of("b1", "a1", "c2", "c3");

What should be the result?

[zhuker]

it seems logical to output b1 c2 c3 in this case
first come first served style
what you say?

[zhuker]

'undefined behavior' is also ok in this case