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From Till Rohrmann <trohrm...@apache.org>
Subject Re: Case style anonymous functions not supported by Scala API
Date Tue, 09 Feb 2016 11:01:01 GMT
Not the DataSet but the JoinDataSet and the CoGroupDataSet do in the form
of an apply function.
​

On Tue, Feb 9, 2016 at 11:09 AM, Stefano Baghino <
stefano.baghino@radicalbit.io> wrote:

> Sure, it was just a draft. I agree that filter and mapPartition make sense,
> but coGroup and join don't look like they take a function.
>
> On Tue, Feb 9, 2016 at 10:08 AM, Till Rohrmann <trohrmann@apache.org>
> wrote:
>
> > This looks like a good design to me :-) The only thing is that it is not
> > complete. For example, the filter, mapPartition, coGroup and join
> functions
> > are missing.
> >
> > Cheers,
> > Till
> > ​
> >
> > On Tue, Feb 9, 2016 at 1:18 AM, Stefano Baghino <
> > stefano.baghino@radicalbit.io> wrote:
> >
> > > What do you think of something like this?
> > >
> > >
> > >
> >
> https://github.com/radicalbit/flink/commit/21a889a437875c88921c93e87d88a378c6b4299e
> > >
> > > In this way, several extensions can be collected in this package object
> > and
> > > picked altogether or a-là-carte (e.g. import
> > > org.apache.flink.api.scala.extensions.AcceptPartialFunctions).
> > >
> > > On Mon, Feb 8, 2016 at 2:51 PM, Till Rohrmann <trohrmann@apache.org>
> > > wrote:
> > >
> > > > I like the idea to support partial functions with Flink’s Scala API.
> > > > However, I think that breaking the API and making it inconsistent
> with
> > > > respect to the Java API is not the best option. I would rather be in
> > > favour
> > > > of the first proposal where we add a new method xxxWith via implicit
> > > > conversions.
> > > >
> > > > Cheers,
> > > > Till
> > > > ​
> > > >
> > > > On Sun, Feb 7, 2016 at 12:44 PM, Stefano Baghino <
> > > > stefano.baghino@radicalbit.io> wrote:
> > > >
> > > > > It took me a little time but I was able to put together some code.
> > > > >
> > > > > In this commit I just added a few methods renamed to prevent
> > > overloading,
> > > > > thus usable with PartialFunction instead of functions:
> > > > >
> > > > >
> > > >
> > >
> >
> https://github.com/radicalbit/flink/commit/aacd59e0ce98cccb66d48a30d07990ac8f345748
> > > > >
> > > > > In this other commit I coded the original proposal, renaming the
> > > methods
> > > > to
> > > > > obtain the same effect as before, but with lower friction for Scala
> > > > > developers (and provided some usage examples):
> > > > >
> > > > >
> > > >
> > >
> >
> https://github.com/radicalbit/flink/commit/33403878eebba70def42f73a1cb671d13b1521b5
> > > > >
> > > > > On Thu, Jan 28, 2016 at 6:16 PM, Stefano Baghino <
> > > > > stefano.baghino@radicalbit.io> wrote:
> > > > >
> > > > > > Hi Stephan,
> > > > > >
> > > > > > thank you for the quick reply and for your feedback; I agree
with
> > you
> > > > > that
> > > > > > breaking changes have to taken very seriously.
> > > > > >
> > > > > > The rationale behind my proposal is that Scala users are already
> > > > > > accustomed to higher-order functions that manipulate collections
> > and
> > > it
> > > > > > would beneficial for them to have an API that tries to adhere
as
> > much
> > > > as
> > > > > > possible to the interface provided by the Scala Collections
API.
> > IMHO
> > > > > being
> > > > > > able to manipulate a DataSet or DataStream like a Scala
> collection
> > > > > > idiomatically would appeal to developers and reduce the friction
> > for
> > > > them
> > > > > > to learn Flink.
> > > > > >
> > > > > > If we want to pursue the renaming path, I think these changes
> (and
> > > > > porting
> > > > > > the rest of the codebase, like `flink-ml` and `flink-contrib`,
to
> > the
> > > > new
> > > > > > method names) can be done in relatively little time. Since Flink
> is
> > > > > > approaching a major release, I think it's a good time to consider
> > > this
> > > > > > change, if the community deems it relevant.
> > > > > >
> > > > > > While we await for feedback on the proposal, I can start working
> on
> > > > both
> > > > > > paths to see how it would affect the codebase, what do you think?
> > > > > >
> > > > > > On Thu, Jan 28, 2016 at 2:14 PM, Stephan Ewen <sewen@apache.org>
> > > > wrote:
> > > > > >
> > > > > >> Hi!
> > > > > >>
> > > > > >> Would be nice to support that, agreed.
> > > > > >>
> > > > > >> Such a fundamental break in the API worries me a bit, though
- I
> > > would
> > > > > opt
> > > > > >> for a non-breaking addition.
> > > > > >> Wrapping the RichFunctions into Scala functions (which are
> > actually
> > > > > >> wrapped
> > > > > >> as rich functions) with implicits seems like a workaround
for
> > > > something
> > > > > >> that should be very simple. Would probably also cost a bit
of
> > > > > performance.
> > > > > >>
> > > > > >>
> > > > > >> I like the idea of "mapWith(...)" - if that were a simple
non
> > > > overloaded
> > > > > >> function accepting a Scala function, it should accept case-style
> > > > > >> functions,
> > > > > >> right?
> > > > > >> Simply adding that would probably solve things, but add
a second
> > > > variant
> > > > > >> of
> > > > > >> each function to the DataSet. An implicit conversion from
> DataSet
> > to
> > > > > >> DataSetExtended (which implements the mapWith, reduceWith,
...)
> > > > methods
> > > > > >> could help there...
> > > > > >>
> > > > > >> What do you think?
> > > > > >>
> > > > > >> Greetings,
> > > > > >> Stephan
> > > > > >>
> > > > > >>
> > > > > >> On Thu, Jan 28, 2016 at 2:05 PM, Stefano Baghino <
> > > > > >> stefano.baghino@radicalbit.io> wrote:
> > > > > >>
> > > > > >> > Hello everybody,
> > > > > >> >
> > > > > >> > as I'm getting familiar with Flink I've found a possible
> > > improvement
> > > > > to
> > > > > >> the
> > > > > >> > Scala APIs: in Scala it's a common pattern to perform
tuple
> > > > extraction
> > > > > >> > using pattern matching, making functions working on
tuples
> more
> > > > > >> readable,
> > > > > >> > like this:
> > > > > >> >
> > > > > >> > // referring to the mail count example in the training
> > > > > >> > // assuming `mails` is a DataSet[(String, String)]
> > > > > >> > // a pair of date and a string with username and email
> > > > > >> > val monthsAndEmails =
> > > > > >> >   mails.map {
> > > > > >> >     case (date, sender) =>
> > > > > >> >       (extractMonth(date), extractEmail(sender))
> > > > > >> >   }
> > > > > >> >
> > > > > >> > However, this is not possible when using the Scala
APIs
> because
> > of
> > > > the
> > > > > >> > overloading of the `map` function in the `DataSet`
and
> > > `DataStream`
> > > > > >> classes
> > > > > >> > (along with other higher-order function such as `flatMap`
and
> > > > > >> `filter`). My
> > > > > >> > understanding is that the main reason to have two different
> > > > overloaded
> > > > > >> > functions is to provide support for `RichFunction`s.
> > > > > >> > I've found out there has been some interest around
the issue
> in
> > > the
> > > > > >> past (
> > > > > >> > [FLINK-1159] <
> https://issues.apache.org/jira/browse/FLINK-1159
> > >).
> > > > > >> > In the past couple of days me and my colleague Andrea
have
> tried
> > > > > several
> > > > > >> > ways to address the problem, coming to two possible
solutions:
> > > > > >> >
> > > > > >> >    1. don't overload and use different names, e.g.
`map`
> taking
> > a
> > > > > Scala
> > > > > >> >    function and `mapWith` taking a Flink MapFunction
> > > > > >> >    2. keep only the method taking a Scala function
(which
> would
> > be
> > > > > more
> > > > > >> >    idiomatic from a Scala perspective, IMHO) and providing
an
> > > > implicit
> > > > > >> >    conversion from the Flink function to the Scala
function
> > within
> > > > the
> > > > > >> >    `org.apache.flink.api.scala` package object
> > > > > >> >
> > > > > >> > We've also evaluated several other approaches using
union
> types
> > > and
> > > > > type
> > > > > >> > classes but we've found them to be too complex. Regarding
the
> > two
> > > > > >> > approaches I've cited, the first would imply a breaking
change
> > to
> > > > the
> > > > > >> APIs,
> > > > > >> > while the second is giving me a hard time at figuring
out some
> > > > > >> compilation
> > > > > >> > errors in `flink-libraries` and `flink-contrib` and
as we
> tested
> > > it
> > > > we
> > > > > >> > found out `RichMapFunction`s lose state (possibly because
of
> the
> > > > > double
> > > > > >> > conversion, first to a Scala function, then to a simple
> > > > > `MapFunction`).
> > > > > >> >
> > > > > >> > You can have a look at the code I've written so far
here
> (last 2
> > > > > >> commits):
> > > > > >> > https://github.com/radicalbit/flink/commits/1159
> > > > > >> >
> > > > > >> > We had a little exchange of ideas and thought that
the first
> > > > solution
> > > > > >> would
> > > > > >> > be easier and also interesting from the standpoint
of the
> > > ergonomics
> > > > > of
> > > > > >> the
> > > > > >> > API (e.g. `line mapWith new LineSplitter`) and would
like to
> > > gather
> > > > > some
> > > > > >> > feedback on the feasibility of this change.
> > > > > >> >
> > > > > >> > Would this still be regarded as a relevant improvement?
What
> do
> > > you
> > > > > >> think
> > > > > >> > about it? Do you think there's time to work on them
before the
> > 1.0
> > > > > >> release?
> > > > > >> > What do you think about introducing breaking changes
to make
> > this
> > > > > >> pattern
> > > > > >> > available to Scala users?
> > > > > >> >
> > > > > >> > Thank you all in advance for your feedback.
> > > > > >> >
> > > > > >> > --
> > > > > >> > BR,
> > > > > >> > Stefano Baghino
> > > > > >> >
> > > > > >> > Software Engineer @ Radicalbit
> > > > > >> >
> > > > > >>
> > > > > >
> > > > > >
> > > > > >
> > > > > > --
> > > > > > BR,
> > > > > > Stefano Baghino
> > > > > >
> > > > > > Software Engineer @ Radicalbit
> > > > > >
> > > > >
> > > > >
> > > > >
> > > > > --
> > > > > BR,
> > > > > Stefano Baghino
> > > > >
> > > > > Software Engineer @ Radicalbit
> > > > >
> > > >
> > >
> > >
> > >
> > > --
> > > BR,
> > > Stefano Baghino
> > >
> > > Software Engineer @ Radicalbit
> > >
> >
>
>
>
> --
> BR,
> Stefano Baghino
>
> Software Engineer @ Radicalbit
>

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