Isn't an array of complexes represented by what arrow already supports? In particular, I see at least two valid in-memory representations to use, that depend on what we are going to do with it:
* Struct[re, im] * FixedList[2] In the first case, we have two buffers, [x0, x1, ...] and [y0, y1, ...], in the second case we have 1 buffer, [x0, y0, x1, y1, ...]. The first representation is useful for column-based operations (e.g. taking the real part in case 1 is trivial; requires a copy in the second case), the second representation is useful for row-base operations (e.g. "take" and "filter" require a single pass over buffer 1). Case 2 does not support Re and Im of different physical types (arguably an issue). Both cases support nullability of individual items or combined. What I conclude is that this does not seem to be a problem about a base in-memory representation, but rather on whether we agree on a representation that justifies adding associated metadata to the spec. The case for the complex interval type recently proposed [1] is more compelling to me because a complex ops over intervals usually required all parts of the interval (and thus the "FixedList" representation is more compelling), but each part has a different type. I.e. it is like a "FixedTypedList[int32, int32, int64]", which we do not natively support. [1] https://github.com/apache/arrow/pull/10177 Best, Jorge On Fri, Jun 11, 2021 at 1:48 AM Neal Richardson <neal.p.richard...@gmail.com> wrote: > It might help this discussion and future discussions like it if we could > define how it is determined whether a type should be part of the Arrow > format, an extension type (and what does it mean to say there is a > "canonical" extension type), or just something that a language > implementation or downstream library builds for itself with metadata. I > feel like this has come up before but I don't recall a resolution. > > Examples might also help: are there examples of "canonical extension > types"? > > Neal > > On Thu, Jun 10, 2021 at 4:20 PM Micah Kornfield <emkornfi...@gmail.com> > wrote: > > > > > > > My understanding is that it means having COMPLEX as an entry in the > > > arrow/type_fwd.h Type enum. I agree this would make implementation > > > work in the C++ library much more straightforward. > > > > One idea I proposed would be to do that, and implement the > > > serialization of the complex metadata using Extension types. > > > > > > If this is a maintainable strategy for Canonical types it sounds good to > > me. > > > > On Thu, Jun 10, 2021 at 4:02 PM Wes McKinney <wesmck...@gmail.com> > wrote: > > > > > My understanding is that it means having COMPLEX as an entry in the > > > arrow/type_fwd.h Type enum. I agree this would make implementation > > > work in the C++ library much more straightforward. > > > > > > One idea I proposed would be to do that, and implement the > > > serialization of the complex metadata using Extension types. > > > > > > On Thu, Jun 10, 2021 at 5:47 PM Weston Pace <weston.p...@gmail.com> > > wrote: > > > > > > > > > While dedicated types are not strictly required, compute functions > > > would > > > > > be much easier to add for a first-class dedicated complex datatype > > > > > rather than for an extension type. > > > > @pitrou > > > > > > > > This is perhaps a naive question (and admittedly, I'm not up to speed > > > > on my compute kernels) but why is this the case? For example, if > > > > adding a complex addition kernel it seems we would be talking > about... > > > > > > > > dest_scalar.real = scalar1.real + scalar2.real; > > > > dest_scalar.im = scalar1.im + scalar2.im; > > > > > > > > vs... > > > > > > > > dest_scalar[0] = scalar1[0] + scalar2[0]; > > > > dest_scalar[1] = scalar1[1] + scalar2[1]; > > > > > > > > On Thu, Jun 10, 2021 at 11:27 AM Wes McKinney <wesmck...@gmail.com> > > > wrote: > > > > > > > > > > I'd be supportive of starting with this as a "canonical" extension > > > > > type so that all implementations are not expected to support > complex > > > > > types — this would encourage us to build sufficient integration > e.g. > > > > > with NumPy to get things working end-to-end with the on-wire > > > > > representation being an extension type. We could certainly choose > to > > > > > treat the type as "first class" in the C++ library without it being > > > > > "top level" in the Type union in Flatbuffers. > > > > > > > > > > I agree that the use cases are more specialized, and the fact that > we > > > > > haven't needed it until now (or at least, its absence suggests > this) > > > > > shows that this is the case. > > > > > > > > > > On Thu, Jun 10, 2021 at 4:17 PM Micah Kornfield < > > emkornfi...@gmail.com> > > > wrote: > > > > > > > > > > > > > > > > > > > > I'm convinced now that first-class types seem to be the way to > > go > > > and I'm > > > > > > > happy to take this approach. > > > > > > > > > > > > I agree from an implementation effort it is simpler, but I'm > still > > > not > > > > > > convinced that we should be adding this as a first class type. > As > > > noted in > > > > > > the survey below it appears Complex numbers are not a core > concept > > > in many > > > > > > general purpose coding languages and it doesn't appear to be a > > > common type > > > > > > in SQL systems either. > > > > > > > > > > > > The reason why I am being nit-picky here is I think that having a > > > first > > > > > > class type indicates that it should eventually be supported by > all > > > > > > reference implementations. An "well known" extension type I > think > > > offers > > > > > > less guarantees which makes it seem more suitable for niche > types. > > > > > > > > > > > > > I don't immediately see a Packed Struct type. Would this need > to > > be > > > > > > > > implemented? > > > > > > > Not necessarily (*). But before thinking about implementation, > > > this > > > > > > > proposal must be accepted into the format. > > > > > > > > > > > > > > > > > > Yes, this is a type that has been proposed in the past and I > think > > > handles > > > > > > a lot of types not yet in Arrow but have been requested (e.g. IP > > > > > > Addresses, Geo coordinates), etc. > > > > > > > > > > > > On Thu, Jun 10, 2021 at 1:06 AM Simon Perkins < > > > simon.perk...@gmail.com> > > > > > > wrote: > > > > > > > > > > > > > On Wed, Jun 9, 2021 at 7:56 PM Antoine Pitrou < > > anto...@python.org> > > > wrote: > > > > > > > > > > > > > > > > > > > > > > > Le 09/06/2021 à 17:52, Micah Kornfield a écrit : > > > > > > > > > > > > > > > > > > Adding a new first-class type in Arrow requires working > > > integration > > > > > > > tests > > > > > > > > > between C++ and Java libraries (once the idea is informally > > > agreed > > > > > > > upon) > > > > > > > > > and then a final vote for approval. We haven't formalized > > > extension > > > > > > > > types > > > > > > > > > but I imagine a similar cross language requirement would be > > > agreed > > > > > > > upon. > > > > > > > > > Implementation of computation wouldn't be required for > adding > > > a new > > > > > > > type. > > > > > > > > > Different language bindings have taken different approaches > > on > > > how much > > > > > > > > > additional computational elements are packaged in them. > > > > > > > > > > > > > > > > While dedicated types are not strictly required, compute > > > functions would > > > > > > > > be much easier to add for a first-class dedicated complex > > > datatype > > > > > > > > rather than for an extension type. > > > > > > > > > > > > > > > > Since complex numbers are quite common in some domains, and > > > since they > > > > > > > > are conceptually simply, IMHO it would make sense to add them > > to > > > the > > > > > > > > native Arrow datatypes (at least COMPLEX64 and COMPLEX128). > > > > > > > > > > > > > > > > > > > > > > I'm convinced now that first-class types seem to be the way to > > go > > > and I'm > > > > > > > happy to take this approach. > > > > > > > Regarding compute functions, it looks like the standard set of > > > scalar > > > > > > > arithmetic and reduction functionality > > > > > > > is desirable for complex numbers: > > > > > > > https://arrow.apache.org/docs/cpp/compute.html# > > > > > > > Perhaps it would be better to split the addition of the Types > and > > > addition > > > > > > > Compute functionality into separate PRs? > > > > > > > > > > > > > > Regarding the process for managing this PR, it sounds like a > > > proposal must > > > > > > > be voted on? > > > > > > > i.e. is this proposal still in this phase > > > > > > > > > > > > > http://arrow.apache.org/docs/developers/contributing.html#before-starting > > > > > > > Regards > > > > > > > > > > > > > > Simon > > > > > > > > > > > > >
