> From: "Remi Forax" <fo...@univ-mlv.fr>
> To: "David Alayachew" <davidalayac...@gmail.com>
> Cc: "core-libs-dev" <core-libs-dev@openjdk.org>
> Sent: Wednesday, January 10, 2024 8:19:15 AM
> Subject: Re: Gatherers -- conditionalWindowFixed?
> Hello David,
> testing the gatherer api, I also wanted a "window" operation as the one you
> are
> describing.
> My use cases is a text file with some sections containing items organized like
> this
> :section1
> item1
> item2
> item3
> :section2
> item1
> item2
> ...
> For me the signature of such method, windowGroupBy??, should take a Predicate
> (is a section, so the reverse of what you are suggesting) and a function that
> take a value (for which the predicate is true) and return a Collector,
> so I can write something like
> record Section(String name, List<String> items) {}
> String input = ...
> List<Section> sections = input.lines()
> .gather(Gatherers.windowGroupBy(line -> line.startsWith(":"), name ->
> Collectors. collectingAndThen (Collectors.toList(), list -> new
> Section(name.substring(1), list))))
> .toList();
Thinking a little more, having a function that returns a Collector is a kind of
an anti-pattern, it would be better to decouple the function that creates the
section and the collector, so the same collector is re-used.
So windowGroupBy?? should take a predicate, a collector and a function that
takes the value (for which the predicate is true) and the result of the
collector.
< T , R , R2 > Gatherer < T , ?, R2 > windowGroupBy ( Predicate <? super T >
predicate , Collector <? super T , ?, ? extends R > collector , BiFunction <?
super T , ? super R , ? extends R2 > mapper )
Rémi
>> From: "David Alayachew" <davidalayac...@gmail.com>
>> To: "core-libs-dev" <core-libs-dev@openjdk.org>
>> Sent: Wednesday, January 10, 2024 7:19:26 AM
>> Subject: Re: Gatherers -- conditionalWindowFixed?
>> And this may also be better named as a split method instead of the long
>> conditionalWindowFixed.
>> On Wed, Jan 10, 2024 at 1:17 AM David Alayachew < [
>> mailto:davidalayac...@gmail.com | davidalayac...@gmail.com ] > wrote:
>>> Oh, I made a mistake. Let me try it again.
>>> If the predicate is true, add the element to the current list (create list
>>> prior
>>> if needed). Else if the predicate is false, send the list down to the
>>> stream,
>>> then add the element to a new list (the new current list, if you will).
>>> On Wed, Jan 10, 2024 at 1:05 AM David Alayachew < [
>>> mailto:davidalayac...@gmail.com | davidalayac...@gmail.com ] > wrote:
>>>> Hello Core Libs Dev Team,
>>>> I have been reading through JEP 461 ( [ https://openjdk.org/jeps/461 |
>>>> https://openjdk.org/jeps/461 ] ) about Gatherers, and I'm really excited
>>>> for
>>>> what this will enable for us.
>>>> By far, the most important functionality that this API facilitates is the
>>>> ability to create windows. Anytime I needed a window, I was basically
>>>> forced to
>>>> use a for loop. Now, the 2 most common window cases are being handed to us
>>>> for
>>>> free. It is very much appreciated.
>>>> Could we add one more method for a conditionalWindowFixed? We would need
>>>> to pass
>>>> in some Predicate<T>. If the predicate returns true, create a list (if it
>>>> does
>>>> not already exist) then add the element to it. If the predicate returns
>>>> false
>>>> while the list is empty, then just move along to the next. Else if the
>>>> predicate returns false while the list is non empty, pass the list down
>>>> into
>>>> the stream. So, you end up with Stream<T> -----> Stream<List<T>>.
>>>> The reason I think this is worth adding is because it facilitates a really
>>>> common use case. We may not want all windows to be the same size.
>>>> Is this something worth adding to the Gatherers API?
>>>> Thank you for your time and help!
>>>> David Alayachew
