Possible groupingBy simplification?

[Joe Bowbeer]

On a positive note, the shining example would be unchanged by this proposal:

  Map<Buyer, Map<Seller, Transaction>>
    biggestTransactionByBuyerSelle**r =
      stream.collect(groupingBy(Txn:**:buyer,
                                groupingBy(Txn::seller,
                                           maxBy(comparing(Txn::amount))

I suggest leading users to the general form by illustrating the equivalence
in the groupingBy(f) documentation.



On Tue, Apr 9, 2013 at 2:56 PM, Joe Bowbeer <joe.bowbeer at gmail.com> wrote:

> I like the most popular form.  In fact, I think it's the only one that
> I've used.
>
> The argument that users will gain by removing their most common form seems
> kind of far-fetched.
>
> In my experience, I do a ctrl-space and look for my target return type on
> the right-hand-side of the IDE popup, and then I try to fill in the missing
> information, such as parameters.  In this case, having to provide toList()
> would probably be a stumbling block for me, as the IDE is not as good when
> it comes to suggesting expressions for parameters.
>
> I sort of like the symmetry with collect(toList()) but not enough to make
> up for the loss.
>
>
>
> On Tue, Apr 9, 2013 at 2:16 PM, Brian Goetz <brian.goetz at oracle.com>wrote:
>
>> Paul suggested the following possible simplification for groupingBy.  It
>> is somewhat counterintuitive at first glance, in that it removes the most
>> commonly used form (!), but might make things easier to grasp in the long
>> run (aided by good docs.)
>>
>> Recall we currently have four forms of groupingBy:
>>
>>     // classifier only -- maps keys to list of matching elements
>>     Collector<T, Map<K, List<T>>>
>>     groupingBy(Function<? super T, ? extends K> classifier)
>>
>>     // Like above, but with explicit map ctor
>>     <T, K, M extends Map<K, List<T>>>
>>     Collector<T, M>
>>     groupingBy(Function<? super T, ? extends K> classifier,
>>                Supplier<M> mapFactory)
>>
>>     // basic cascaded form
>>     Collector<T, Map<K, D>>
>>     groupingBy(Function<? super T, ? extends K> classifier,
>>                Collector<T, D> downstream)
>>
>>     // cascaded form with explicit ctor
>>     <T, K, D, M extends Map<K, D>>
>>     Collector<T, M>
>>     groupingBy(Function<? super T, ? extends K> classifier,
>>                Supplier<M> mapFactory,
>>                Collector<T, D> downstream)
>>
>> Plus four corresponding forms for groupingByConcurrent.
>>
>> The first form is likely to be the most common, as it is the traditional
>> "group by".  It is equivalent to:
>>
>>   groupingBy(classifier, toList());
>>
>> The proposal is: Drop the first two forms.  Just as users can learn that
>> to collect elements into a list, you do:
>>
>>   collect(toList())
>>
>> people can learn that to do the simple form of groupBy, you can do:
>>
>>   collect(groupingBy(f, toList());
>>
>> Which also reads perfectly well.
>>
>> By cutting the number of forms in half, it helps users to realize that
>> groupingBy does just one thing -- classifies elements by key, and collects
>> elements associated with that key.  Obviously the docs for groupingBy can
>> show examples of the simple grouping as well as more sophisticated
>> groupings.
>>
>>
>
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