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Re: Stream question

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On 3/15/2016 4:21 PM, Sebastian wrote:
> Am 15.03.2016 19:11, schrieb Rhino:
> [example snipped]
>>
>> How do I adjust what I have to get the number of orders for each agency
>> code?
>>
>
> Two possibilities come to my mind.
>
> (A) This answers your question of how to adjust what you have.
>
> On Feb 22nd I posted in this group in the thread "stream filter twice",
> see
> https://groups.google.com/d/msg/comp.lang.java.programmer/zSqNcCNDCRI/mmeBA3w0DQAJ
>
>
> In that post I discuss the possibility of using a so-called "combining
> collector" from the library jool (https://github.com/jOOQ/jOOL). In your
> case, such a collector would apply two downstream collectors
> simultaneously and return a pair of results:
>
> // untested
> Map<String, Tuple2<Integer, Long>> salesByAgency
>             = ticketOrders.stream()
>                 .collect(groupingBy(TicketSale::getAgencyCode,
>                          Tuple.collectors(
>                             summingInt(TicketSale::getTicketsSold),
>                             counting())));
>
> If you don't want the dependency on the library, it is easy to write the
> collector yourself, see the post cited.
>
> Notes:
> 1. Questions like this involving processing data from the same stream
> source multiple times in different ways come up very often. Jool
> provides a very neat way to deal with this need. Excellent library.
>
> 2. Besides summing, you can also do any other reduction using
> Collectors.reducing() as one of the downstream collectors.
>
I have to admit I'm not keen on using an extra library. It just seems 
like something else to learn. (And maintain. And install everywhere my 
program runs.) I'm sure it's as great a library as you say it is but 
your second solution is the one I prefer, at least so far. As I learn 
more, I may develop a preference for Jool ;-)
>
> (B) This does not adjust what you have, but is a different (and much
> simpler) way to do it.
>
> Map<String, IntSummaryStatistics> salesByAgency
>      = ticketOrders.stream()
>          .collect(groupingBy(TicketSale::getAgencyCode,
>                  Collectors.summarizingInt(TicketSale::getTicketsSold)));
>
> IntSummaryStatistics has methods getCount() and getSum().

I really like this! It's nice and simple to look at and when I ran it in 
debug, it worked very nicely and produced the result I wanted. The only 
negative is that it returns two statistics that I don't need and I'm 
probably paying something for that but the volumes of data I am 
processing are very low so I don't see any extra expense as significant. 
(It might be if I were processing millions of records but I'm only going 
to have dozens most of the time.)

Thank you VERY much for this solution!

I've got a lot to learn but this will help me get off to a good start as 
I try to understand streams and stream handling.

-- 
Rhino

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Stream question Rhino <no_offline_contact@example.com> - 2016-03-15 14:11 -0400
  Re: Stream question Sebastian <news@seyweiler.dyndns.org> - 2016-03-15 21:21 +0100
    Re: Stream question Rhino <no_offline_contact@example.com> - 2016-03-16 00:44 -0400

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