Is there an aggregateBy method in the stream Java 8 api?

Question

Run across this very interesting but one year old presentation by Brian Goetz - in the slide linked he presents an aggregateBy() method supposedly in the Stream

Answer 1

The aggregate operation can be done using the Collectors class. So in the video, the example would be equivalent to :

Map map = 
    documents.stream().collect(Collectors.groupingBy(Document::getAuthor, Collectors.summingInt(Document::getPageCount)));

The groupingBy method will give you a Map>. Now you have to use a downstream collector to sum all the page count for each document in the List associated with each key.

This is done by providing a downstream collector to groupingBy, which is summingInt, resulting in a Map.

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They give basically the same example in the documentation where they compute the sum of the employees' salary by department.

I think that they removed this operation and created the Collectors class instead to have a useful class that contains a lot of reductions that you will use commonly.