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From Josh Wills <josh.wi...@gmail.com>
Subject Re: Alternative strategy for incorporating Java 8 lambdas into Crunch
Date Tue, 15 Dec 2015 01:04:48 GMT
On Mon, Dec 14, 2015 at 4:15 PM, David Whiting <davidwhiting@gmail.com>
wrote:

> 1) Not at all, just some leftover working names for stuff.
>
> 2) Not for a totally minimal implementation, but some of the features I
> would like to include would rely on Java 8 things, for example adapting the
> GroupedTable stuff to use Streams rather than Iterables because of a) the
> extra expressivity and b) the implied once-only traversal. We could have a
> filterMap which applies a Function<S, Optional<T>> (my most common use case
> for a DoFn instead of a MapFn at the moment). We can also potentially
> utilise Collectors for collapsing values in reduce-side stuff and finally,
> it'll make the implementation of it a fair bit easier. The maven overhead
> is pretty low, so I guess it's just the existence of an extra artifact to
> consider. The way I see it is that it's a push to make the API feel more
> like Java streams and be more immediately usable by someone who knows Java
> streams but not necessarily big data, so the more we can replicate that
> feel by integrating with other familiar Java 8 features, the better.
>

Makes sense to me. +1 for a new crunch-lambda module.


>
> On 15 December 2015 at 00:51, Josh Wills <josh.wills@gmail.com> wrote:
>
> > I think I lean towards the collections approach, but that's probably
> > because of my Scrunch experience. Two questions:
> >
> > 1) Is mapToTable necessary? I would think map(SFunction, PTableType)
> would
> > be distinguishable from map(SFunction, PType) by the compiler in the same
> > way it is for parallelDo.
> > 2) Does the collections approach need a separate maven target at all, or
> > could it just be part of crunch-core as a replacement for the IFn stuff?
> Or
> > is there Java 8-only stuff we'll want to add in to its API?
> >
> > On Mon, Dec 14, 2015 at 3:13 PM, David Whiting <davw@apache.org> wrote:
> >
> > > Ok, so I've implemented a few iterations of this. I went forward with
> the
> > > "wrap the functions" method, which seemed to work alright, but finding
> > good
> > > names for functions which essentially just wrap functions but which
> > aren't
> > > ambiguous in erasure and read nicely was a real challenge. I showed
> some
> > > sample code to some of my fellow data engineers and the consensus
> seemed
> > to
> > > be that it was definitely better than anonymous inner classes, but it
> > still
> > > felt kind of awkward and strange to use.
> > >
> > > So here's a 3rd option: wrap the collection types rather than the
> > function
> > > types, and present an API which feels truly Java 8 native whilst still
> > > being able to dig back to the underlying PCollections (doing pretty
> much
> > > what Scrunch does, but with less implicit Scala magic).
> > >
> > > Here's a super-minimal proof-of-concept for that:
> > > https://gist.github.com/DavW/7efe484ea0c00cf6e66b
> > >
> > > and a comparison of the two approaches in usage:
> > > https://gist.github.com/DavW/997a92b31d55c5317fb7
> > >
> > >
> > > On 13 December 2015 at 16:14, Gabriel Reid <gabriel.reid@gmail.com>
> > wrote:
> > >
> > > > This looks very cool. As long as we can keep things compatible with
> > > > Java 7 using whatever kind of maven voodoo that's necessary, I'm all
> > > > for it.
> > > >
> > > > I'd say no real reason to keep the IFn stuff if this goes in.
> > > >
> > > > - Gabriel
> > > >
> > > > On Fri, Dec 11, 2015 at 11:18 PM, Josh Wills <josh.wills@gmail.com>
> > > wrote:
> > > > > It seems like a net positive over the IFn stuff, so I could make
an
> > > > > argument for replacing it, but if there's anyone out there in love
> > > > w/IFns,
> > > > > they should speak up now. :)
> > > > >
> > > > > J
> > > > >
> > > > > On Fri, Dec 11, 2015 at 2:17 PM, David Whiting <davw@apache.org>
> > > wrote:
> > > > >
> > > > >> I *think* you can set language level and target jdk on a
> per-module
> > > > basis,
> > > > >> so it should be relatively easy. I'll experiment at some point
> over
> > > the
> > > > >> weekend. Would this complement or replace the I*Fn stuff do you
> > think?
> > > > 14.0
> > > > >> is not yet released, so I guess it's not too late to change if
we
> > want
> > > > to.
> > > > >>
> > > > >> On 11 December 2015 at 22:57, Josh Wills <josh.wills@gmail.com>
> > > wrote:
> > > > >>
> > > > >> > That's the sexiest thing I've seen in some time. +1 for
a lambda
> > > > module,
> > > > >> > but how does that work in Maven-fu? Is it like a conditional
> > compile
> > > > or
> > > > >> > something?
> > > > >> >
> > > > >> > On Fri, Dec 11, 2015 at 1:20 PM, David Whiting <davw@apache.org
> >
> > > > wrote:
> > > > >> >
> > > > >> > > Oops, my bad. Here's a Gist:
> > > > >> > > https://gist.github.com/DavW/e2588e42c45ad8c06038
> > > > >> > >
> > > > >> > > On 11 December 2015 at 18:43, Josh Wills <
> josh.wills@gmail.com>
> > > > wrote:
> > > > >> > >
> > > > >> > > > I think it's kind of awesome, but the attachment
didn't go
> > > > through-
> > > > >> PR
> > > > >> > or
> > > > >> > > > gist?
> > > > >> > > > On Fri, Dec 11, 2015 at 7:42 AM David Whiting
<
> > davw@apache.org>
> > > > >> wrote:
> > > > >> > > >
> > > > >> > > > > While fixing the bug where the IFn version
of mapValues on
> > > > >> > > PGroupedTable
> > > > >> > > > > was missing, I got thinking that this is
quite an
> > inefficient
> > > > way
> > > > >> of
> > > > >> > > > > including support for lambdas and method
references, and
> it
> > > > still
> > > > >> > > didn't
> > > > >> > > > > actually support quite a few of the features
that would
> make
> > > it
> > > > >> easy
> > > > >> > to
> > > > >> > > > > code against.
> > > > >> > > > >
> > > > >> > > > > Negative parts of existing lambda implementation:
> > > > >> > > > > 1) Explosion of already-crowded PCollection,
PTable and
> > > > >> PGroupedTable
> > > > >> > > > > interfaces, and having to implement those
methods in all
> > > > >> > > implementations.
> > > > >> > > > > 2) Not supporting flatMap to Optional or
Stream types.
> > > > >> > > > > 3) Not exposing convenient types for reduce-type
> operations
> > > > (Stream
> > > > >> > > > > instead of Iterable, for example).
> > > > >> > > > >
> > > > >> > > > > Something that would solve all three of these
is to build
> > > lambda
> > > > >> > > support
> > > > >> > > > > as a separate artifact (so we can use all
java8 types),
> and
> > > > instead
> > > > >> > of
> > > > >> > > > the
> > > > >> > > > > API being directly on the PSomething interfaces,
we just
> > have
> > > > >> > > convenient
> > > > >> > > > > ways to wrap up lambdas into DoFns or MapFns
via
> > > > >> statically-imported
> > > > >> > > > > methods.
> > > > >> > > > >
> > > > >> > > > > The usage then becomes
> > > > >> > > > > import static org.apache.crunch.Lambda.*;
> > > > >> > > > > ...
> > > > >> > > > > someCollection.parallelDo(flatMap(d ->
someFnOf(d)), pt)
> > > > >> > > > > ...
> > > > >> > > > > otherGroupedTable.mapValue(reduce(seq ->
seq.mapToInt(i ->
> > > > >> i).sum()),
> > > > >> > > > > ints())
> > > > >> > > > >
> > > > >> > > > > Where flatMap and reduce are static methods
on Lambda, and
> > > > Lambda
> > > > >> > goes
> > > > >> > > in
> > > > >> > > > > it's own artifact (to preserve compatibility
with 6 and 7
> > for
> > > > the
> > > > >> > rest
> > > > >> > > of
> > > > >> > > > > Crunch).
> > > > >> > > > > I've attached a basic proof-of-concept implementation
> which
> > > I've
> > > > >> > > tested a
> > > > >> > > > > few things with, and I'm very happy to sketch
out a more
> > > > >> substantial
> > > > >> > > > > implementation if people here think it's
a good idea in
> > > general.
> > > > >> > > > >
> > > > >> > > > > Thoughts? Ideas? Suggestions? Please tell
me if this is
> > crazy.
> > > > >> > > > >
> > > > >> > > > >
> > > > >> > > >
> > > > >> > >
> > > > >> >
> > > > >>
> > > >
> > >
> >
>

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