I'm using javascript as an adjective, sorry about the confusion Paul. And
maybe JSON would be a better adjective (but neither is good).
With your example of two Binary vectors that have different metadata, yes
the single-primitive model would argue that they should either be a single
binary vector or a struct that indicates the type. However the counter I
outlined above is that you could say single-primitive is really
single-container and unique leaf--e.g. int32,int64 is allowed but
int32,int32 is not and thus binary(md1), binary(md2) would be allowed. In
this context we could treat metadata as part of the leaf node type
signature.
Random aside, given your description I'm wondering if you're using
DenseUnion because you really need a DenseStruct.
On Tue, Mar 20, 2018 at 12:18 PM, Paul Taylor <ptay...@apache.org> wrote:
> Jumping in b/c I did the JS Union implementations. I inferred the behavior
> from what I understood the C++ and Java to be doing, so I may have
> misunderstood how they should work.
>
> > To that end, we talked about
> > introducing a "single-primitive" (a.k.a. "javascript") union behavior
> that
> > would operate this way.
>
>
> Just to clarify, Jacques: are you referencing how the ArrowJS Unions work
> today, or using JavaScript as an adjective to describe the behavior you'd
> like to see?
>
> If the former, I may have misunderstood the distinction between Dense and
> Sparse Unions (typeIds buffer maps idx -> child_id, with Dense including a
> valueOffsets buffer to also map idx -> child_idx). I'm happy to review the
> implementations if this behavior is incorrect.
>
> > It would be defined by only allowing one of each
> > variety of type at any intermediate node of hierarchy. In other words, a
> > struct could never contain two structs or two lists. (It also couldn't
> > contain two int64 or int32). This is how the Java library behaves.
>
>
> One way we use the JS Union implementation at Graphistry is representing a
> heterogenous Struct of IPv4/6 address + port number combinations:
>
> > interface IPv4 extends BinaryVector { metadata: { ipVersion: 4 } }
> > interface IPv6 extends BinaryVector { metadata: { ipVersion: 6 } }
> >
> > type IPAddresses = DenseUnion<IPv4 | IPv6>
> > type IPsAndPorts = Struct<[IPAddress, Int32 /* <- nullable port vector
> */]>
>
> In this case, we benefit from the ability to compact the IP addresses into
> a dense Binary Vectors, with DenseUnion's valueOffsets buffer acting as an
> implicit Dictionary encoding -- useful when representing 200k events on an
> internal network of say, ~200 IPs.
>
> Would the "single-primitive" proposal restrict the IPAddresses type from
> containing two child Binary Vectors?
>
>
> > On Mar 20, 2018, at 10:05 AM, Jacques Nadeau <jacq...@apache.org> wrote:
> >
> >>
> >> I may have missed something, but I'm not remembering either the points
> >> re: JavaScript or decimals. My understanding is that we have been
> >> discussing how to handle a union-of-complex-types -- the Union
> >> implementation in Java does not support this. Could you clarify or
> >> refer to prior mailing list threads?
> >>
> >
> > Sorry, let me clarify.
> >
> > The original thinking was that there is a non-collapsing intermediate
> node
> > behavior and an intermediate node collapsing behavior (a.k.a
> > single-primitive behavior) for unions. For example, if we have the
> > following records and types (imagine two different sensors generations):
> >
> > sensor_gen1: {
> > ts: <timestamp(nanos)>,
> > info: {
> > metric: <utf8>,
> > value: <double>,
> > variance: <double>
> > }
> > }
> >
> > (a.k.a. struct<
> > ts:timestamp(nanos),
> > info: struct<
> > metric: utf8,
> > value: double,
> > variance: double
> >>
> >> )
> >
> > sensor_gen2: {
> > ts: <timestamp(nanos)>
> > info: {
> > metric: <utf8>
> > value: <int64>
> > tolerance: <double>
> > }
> > }
> >
> > (a.k.a struct<
> > ts:timestamp(nanos),
> > info: struct<
> > metric: utf8,
> > value: int64,
> > tolerance: double
> >>
> >> )
> >
> >
> > We have two possible unions that could be created:
> >
> > the non-node-collapsing behavior:
> > struct<
> > ts:timestamp(nanos),
> > info: union<
> > struct<
> > metric: utf8,
> > value: double,
> > variance: double
> >> ,
> > struct<
> > metric: utf8,
> > value: int64,
> > tolerance: double
> >>
> >>
> >>
> >
> > Or the collapsing behavior
> >
> > struct<
> > ts:timestamp(nanos),
> > info: union<
> > info: struct<
> > metric: utf8,
> > value: union<double, int64>,
> > tolerance: double
> > variance: double
> >>
> >>
> >
> > For generalized data processing (e.g. a sql system), I consider the
> latter
> > to be optimal as it allows analysts to deal with sameness without having
> to
> > dereference to a particular union branch. To that end, we talked about
> > introducing a "single-primitive" (a.k.a. "javascript") union behavior
> that
> > would operate this way. It would be defined by only allowing one of each
> > variety of type at any intermediate node of hierarchy. In other words, a
> > struct could never contain two structs or two lists. (It also couldn't
> > contain two int64 or int32). This is how the Java library behaves. The
> > format simplification that is then possible would be that these names
> would
> > be directly mapped to known positions (e.g. struct is always in position
> 1
> > and list is always in position 2, etc.). The java library doesn't try to
> do
> > the latter at the moment (it used to but the definition wasn't clear).
> >
> > The single-primitive behavior in general works very well. It also doesn't
> > limit a user from having a set of multiple unions that they want to
> > dereference but does require that each of those branches are named via a
> > struct rather than using positions in unions. In other words, it doesn't
> > allow for positional union dereferencing. The one place where it becomes
> > challenging is when a leaf node is not simple. For example decimal(30,2)
> > combined with decimal(30,4). In this case, what should the behavior be?
> > Following a simple-primitive model would suggest that this is only
> possible
> > if you named them e.g. struct<dec30_2: decimal(30,2), dec30_4:
> > decimal(30,4)> but that seems arbitrary since I can also create
> > union<int32,int64> (which feels very much the same). The problem
> compounds
> > as we have added more information at other leaf types (e.g.
> > timestamp(millis) and timestamp(nanos)).
> >
> > So, my suggestion that started the thread was that this single-primitive
> > behavior not be part of the format but be a choice of the implementation.
> > In terms of the way to expose the union of structs scenario in Java, I
> > propose that we implement that as named structs for now and enhance the
> > behavior if people have use cases that need alternative apis (and are
> > willing to invest in an arbitrary approach without disrupting the
> existing
> > apis).
> >
> >
> >>> - Interval Day to Seconds: 8 bytes representing number of
> >>> milliseconds.
> >>> - Interval Year to Months: 4 bytes representing number of months.
> >>
> >> Yes, I'm supportive of this. The one addition is that we need to add a
> >> "unit" field to the metadata to support finer granularity than
> >> milliseconds -- the idea is that we should support the same units as
> >> TImestamp so that a difference of timestamps produces an interval (aka
> >> timedelta). We have this data arising already in Python, for example,
> >> but we cannot represent it in Arrow at the moment, so this has been a
> >> rough edge for users.
> >>
> >>
> > Agree on units.
>
>
