Equivalent of Maps.uniqueIndex?

[Brian Goetz]

Suggestion: build from source or wait for the next promotion.  What is 
in b69 is probably just wrong.

On 1/4/2013 10:59 AM, Michael Nascimento wrote:
> Ok, here we go.
>
> I can only use build 69. In this build, Tabulator.mappedTo type
> parameters seem to be the other way around.
>
> Assume I have a bunch of entities with a getId() : Long. What I want is:
>
> // with Guava and JDK 8
> Map<Long, Entity> entityById = Maps.uniqueIndex(entities, e -> e.getId());
>
> With pure JDK 8, here is my best attempt:
>
> Map<Long, Entity> entityById =
> entities.parallelStream().tabulate(Tabulators.<Long,Entity>mappedTo(e
> -> e.getId(), (i1, i2) -> i1));
>
> which doesn't work. This:
>
> entities.parallelStream().tabulate(Tabulators.<Entity,Long>mappedTo(e
> -> e.getId(), (i1, i2) -> i1));
>
> compiles, but is pretty useless.
>
> Suggestions?
>
> Regards,
> Michael
>
>
> On Fri, Jan 4, 2013 at 1:41 PM, Brian Goetz <brian.goetz at oracle.com> wrote:
>> Stuff is in flux, apologies.
>>
>> In the current tip, Tabulators became Accumulators, and we have these
>> versions which take a T->U, plus optionally a Supplier<Map> and a merge
>> function (the default throws on duplicates.)
>>
>>      public static <T, U> Accumulator<T, Map<T,U>> mappedTo(Function<? super
>> T, ? extends U> mapper) {
>>          return mappedTo(mapper, (BinaryOperator<U>) THROWING_MERGER);
>>      }
>>
>>      public static <T, U> Accumulator<T, Map<T,U>> mappedTo(Function<? super
>> T, ? extends U> mapper,
>>
>> BinaryOperator<U> mergeFunction) {
>>          return mappedTo(mapper, mergeFunction, (Supplier<Map<T,U>>)
>> HashMap::new);
>>      }
>>
>>      public static <T, U, M extends Map<T, U>> Accumulator<T, M>
>> mappedTo(Function<? super T, ? extends U> mapper,
>>
>>    Supplier<M> mapSupplier) {
>>          return mappedTo(mapper, (BinaryOperator<U>) THROWING_MERGER,
>> mapSupplier);
>>      }
>>      public static <T, U, M extends Map<T, U>> Accumulator<T, M>
>> mappedTo(Function<? super T, ? extends U> mapper,
>>
>>    BinaryOperator<U> mergeFunction,
>>
>>    Supplier<M> mapSupplier) {
>>          return new MergingMapAccumulator<T, T, U, M>(mapSupplier,
>> mergeFunction) {
>>              @Override
>>              public void accumulate(M map, T value) {
>>                  accumulate(map, value, mapper.apply(value));
>>              }
>>          };
>>
>>      }
>>
>>
>> On 1/4/2013 10:37 AM, Michael Nascimento wrote:
>>>
>>> There is no mapTo() in Tabulators in build 69. There is a mappedTo,
>>> but it takes a BinaryOperator. Which one am I supposed to use?
>>>
>>> Regards,
>>> Michael
>>>
>>> On Fri, Jan 4, 2013 at 1:28 PM, Brian Goetz <brian.goetz at oracle.com>
>>> wrote:
>>>>
>>>> tabulate(Tabulators.mapTo())
>>>>
>>>>
>>>> On 1/4/2013 10:22 AM, Michael Nascimento wrote:
>>>>>
>>>>>
>>>>> Guys,
>>>>>
>>>>> What is the equivalent in Lambda to Guava's Maps.uniqueIndex:
>>>>>
>>>>>
>>>>>
>>>>> http://docs.guava-libraries.googlecode.com/git-history/release/javadoc/com/google/common/collect/Maps.html#uniqueIndex(java.lang.Iterable,
>>>>> com.google.common.base.Function)
>>>>>
>>>>> I was trying the tabulate method, but couldn't find a method in
>>>>> Tabulators with a single function that assumes the stream has unique
>>>>> keys.
>>>>>
>>>>> Regards,
>>>>> Michael
>>>>>
>>>>
>>