Lambda it2 - split?

[Brian Goetz]

There are a few ways to do this, depending on the shapes of your data.

One way is:

   people.stream().groupBy(Person::getCity)
                  .reduceValues(...);
  -> yields a Map<City, U> where U is the reduction

Another is

   people.stream().foldBy(Person::getCity,
                          () -> new Averager(),
                          (avg, e) -> avg.updateWith(e))
                  .mapValues(avg -> avg.compute())
                  .into(new HashMap<>());

  -> yields a Map<City, U>

which is probably more efficient.

On 9/13/2012 2:01 AM, Janda Martin wrote:
> Hi,
>
>    I have newbie question. Does lambda streams support some kind of split operation?
>
> Virtual problem:
>
> Input: collection of cities
>    List<City> cityList
>
> Output: average age for all people
>    double avgAge
>
> Steps to solve:
>    1) Each city MAP to collection of people
>    2) Compute AVG over collection of people
>
> I know that I can
> - MAP input value exactly to another value
> - REDUCE collection to one value
>
> But can I?
> - SPLIT input value into 'stream' (not collection) of another values
>
>
> Thank you very much for answer
>
>    Martin
>
> PS Sorry for my bad English. I hope that you understand what I mean.
>