Encounter order

[Andrey Breslav]

Makes sense. Thanks

On 26.10.2012 17:04, Brian Goetz wrote:
> Its the same problem of sensibility that we get with ordinary reduce. 
> If we can only assume the reducer is associative, and we see that the 
> input source structurally has an encounter order, then reordering the 
> elements could result in the wrong answer.  (i.e., it stands to reason 
> that stream.reduce(r) should produce the same result as 
> stream.reduceBy(e -> 1, r).get(1)).
>
> On 10/26/2012 8:55 AM, Andrey Breslav wrote:
>> People don't expect ordering of the *keys*, and that's fine.  What I
>>>>> was talking about was ordering of the values, since the Map returned
>>>>> is a Map<K, Collection<V>>.
>>>> Your reduceBy() looked like this:
>>>>
>>>> <U, W> Map<U, W> reduceBy(...)
>>>>
>>>> no collections anywhere. Was that a mistake?
>>>
>>> groupBy returns a Map<K,Collection<T>>.
>>>
>>> reduceBy returns a Map<K,W>, because instead of accumulating elements
>>> in a K bucket and sticking them in a collection, we reduce all the
>>> elements in the K bucket.
>>>
>>> For example:
>>>
>>>   Map<Author, Document> longestDocByAuthor
>>>     = docs.reduceBy(Document::getAuthor,
>>>                     (d1, d2) -> (d1.length() > d2.length() ? d1 : d2));
>>>
>> Yes. And my point was that thus no ordering considerations are
>> applicable to the result of reduceBy. Or am I missing something?