Support vectors as indices to NamedTuple #32664

cmcaine · 2019-07-24T00:54:45Z

cmcaine · 2019-07-24T01:20:18Z

I think what I should probably do instead of this code is have indexing with a vector return a new named tuple. This matches the subsetting behaviour that tuples and arrays already exhibit when indexed with a vector.

(1, 3, 5, 7)[2:3] == (3, 5)
(x = 1, y = 3, z = 5)[1:1] == (x = 1,)
(x = 1, y = 3, z = 5)[1:2] == (x = 1, y = 3)

andyferris · 2019-07-24T06:42:51Z

@cmcaine I still think the semantics for generalized non-scalar indexing I proposed in the Julep #24019 will be useful and simple to understand, which in this case would mean returning a vector.

Would you consider indexing a named tuple with a named tuple to return a new named tuple as reasonable?

andyferris · 2019-07-24T06:45:34Z

base/namedtuple.jl

@@ -103,6 +103,8 @@ firstindex(t::NamedTuple) = 1
 lastindex(t::NamedTuple) = nfields(t)
 getindex(t::NamedTuple, i::Int) = getfield(t, i)
 getindex(t::NamedTuple, i::Symbol) = getfield(t, i)
+getindex(t::NamedTuple, v::AbstractVector{Symbol}) = [t[i] for i in v]


This maps all v::AbstractVector to Vector.

I wonder if we can make this more generic, as in something like map(Fix1(getindex, t), v)? For example, that definition would mean if v were a SVector then the output could also be a SVector.

Replied below. This seems like a fine implementation if we want to move towards the semantics in your Julep.

andyferris · 2019-07-24T06:46:44Z

base/namedtuple.jl

@@ -103,6 +103,8 @@ firstindex(t::NamedTuple) = 1
 lastindex(t::NamedTuple) = nfields(t)
 getindex(t::NamedTuple, i::Int) = getfield(t, i)
 getindex(t::NamedTuple, i::Symbol) = getfield(t, i)
+getindex(t::NamedTuple, v::AbstractVector{Symbol}) = [t[i] for i in v]
+getindex(t::NamedTuple, i) = values(t)[i]


Can you explain what the semantics of this are? What are some examples where this helps you, and what do you expect as output?

@ararslan suggested the latter as a fallback so that indexing methods for Tuple will be used.

Indexing NamedTuples only differs from that for Tuples when indexing with Symbols. Everything else should be identical, so we can get it all for free by using a fallback like this.

cmcaine · 2019-07-24T10:39:36Z

From the linked issue:

...provide that for out = a[b]:

The output container out shares the indices of b (note: these are CartesianRange for arrays)

The values out[i] correspond to a[b[i]].

Does this describe the behaviour you are suggesting?

nt = (x=1, y=3, z=5)
nt[[1,2]] == nt[1:2] == [1,3]
nt[(1,2)] == (1,2)

nt[(:x, :y)] == (1,2)
nt[[:x, :y]] == [1,2]

nt[(a=:x, b=:z)] == (a=1, b=5)
nt[(x=:x, y=:y)] == (x=1, y=3)

# And not this one (because b does not have the indices :x, :y)
nt[(:x, :y)] == (x=1, y=3)

I think I prefer this last interpretation for a vector of symbols, and maybe (probably not) it is OK because out does share all the indices of b? It just has some extra aliases on top.

I dislike that the current way to subset a namedtuple is NamedTuple{(:x, :y)}((x=1, y=3, z=5)) == (x=1, y=3), but I'm happy with either a subsetting convention or your convention.

What do you think?

cmcaine · 2019-07-24T10:56:44Z

Supporting more exotic vector types does not seem to be free:

julia> map(Base.Fix1(getindex, nt), OffsetVector([:x, :y], -1))
OffsetArray(::Array{Real,1}, 0:1) with eltype Real with indices 0:1:
 #undef
  -1   

julia> map(Base.Fix1(getindex, nt), OffsetVector([:x, :y], 0))
OffsetArray(::Array{Real,1}, 1:2) with eltype Real with indices 1:2:
 π = 3.1415926535897...
 -1                    

julia> map(Base.Fix1(getindex, nt), OffsetVector([:x, :y], 1))
OffsetArray(::Array{Real,1}, 2:3) with eltype Real with indices 2:3:
 π = 3.1415926535897...
 -1                    

julia> map(Base.Fix1(getindex, nt), OffsetVector([:x, :y], 2))
ERROR: BoundsError: attempt to access OffsetArray(::Array{Real,1}, 3:4) with eltype Real with indices 3:4 at index [3:5]
Stacktrace:
 [1] copyto!(::OffsetArray{Real,1,Array{Real,1}}, ::Int64, ::OffsetArray{Irrational{:π},1,Array{Irrational{:π},1}}, ::Int64, ::Int64) at ./abstractarray.jl:785
 [2] collect_to!(::OffsetArray{Irrational{:π},1,Array{Irrational{:π},1}}, ::Base.Generator{OffsetArray{Symbol,1,Array{Symbol,1}},Base.Fix1{typeof(getindex),NamedTuple{(:x, :y, :z),Tuple{Irrational{:π},Int64,Char}}}}, ::Int64, ::Tuple{Base.IdentityUnitRange{UnitRange{Int64}},Int64}) at ./array.jl:641
 [3] collect_to_with_first!(::OffsetArray{Irrational{:π},1,Array{Irrational{:π},1}}, ::Irrational{:π}, ::Base.Generator{OffsetArray{Symbol,1,Array{Symbol,1}},Base.Fix1{typeof(getindex),NamedTuple{(:x, :y, :z),Tuple{Irrational{:π},Int64,Char}}}}, ::Tuple{Base.IdentityUnitRange{UnitRange{Int64}},Int64}) at ./array.jl:630
 [4] _collect(::OffsetArray{Symbol,1,Array{Symbol,1}}, ::Base.Generator{OffsetArray{Symbol,1,Array{Symbol,1}},Base.Fix1{typeof(getindex),NamedTuple{(:x, :y, :z),Tuple{Irrational{:π},Int64,Char}}}}, ::Base.EltypeUnknown, ::Base.HasShape{1}) at ./array.jl:624
 [5] collect_similar(::OffsetArray{Symbol,1,Array{Symbol,1}}, ::Base.Generator{OffsetArray{Symbol,1,Array{Symbol,1}},Base.Fix1{typeof(getindex),NamedTuple{(:x, :y, :z),Tuple{Irrational{:π},Int64,Char}}}}) at ./array.jl:548
 [6] map(::Function, ::OffsetArray{Symbol,1,Array{Symbol,1}}) at ./abstractarray.jl:2018
 [7] top-level scope at none:0

SVectors work.

ararslan · 2019-07-24T18:41:41Z

base/namedtuple.jl

@@ -103,6 +103,8 @@ firstindex(t::NamedTuple) = 1
 lastindex(t::NamedTuple) = nfields(t)
 getindex(t::NamedTuple, i::Int) = getfield(t, i)
 getindex(t::NamedTuple, i::Symbol) = getfield(t, i)
+getindex(t::NamedTuple, v::AbstractVector{Symbol}) = [t[i] for i in v]


I think this is wrong and/or surprising. I'd do it as

Suggested change

getindex(t::NamedTuple, v::AbstractVector{Symbol}) = [t[i] for i in v]

getindex(t::NamedTuple, v::AbstractVector{Symbol}) = (; map(i->i => t[i], t)...)

In particular, indexing a tuple with a vector gives you back a tuple, so by analogy, indexing a named tuple with a vector should give you back a named tuple.

andyferris · 2019-07-25T11:30:09Z

@ararslan I see what you mean by the analogy with tuples, but maybe it wouldn’t surprise you that I think the non-scalar tuple indexing is slightly wrong :)

Basically I’d love to see the language evolve towards the kinds of ideas in #24019 rather than diffuse away from that. The tuple-vector indexing isn’t so bad because it actually preserves the key values (it happens that Vector and Tuple both use one-based indexing). Here, if indexing with a vector returned a named tuple, say, then the keys of the indexer wouldn’t be those of the output.

(Note: I’m also unclear why named tuples need two sets of indices - symbols and integers - when values is convenient for getting it as a Tuple)

cmcaine · 2019-07-25T11:33:34Z

I feel like there needs to be consensus on what outputs to expect from the test cases I listed in order to continue.

Here are those test cases from the earlier comment with outputs as I imagined appropriate for the rule that @andyferris suggested in their Julep:

nt = (x=1, y=3, z=5)
nt[[1,2]] == [1,3]
nt[(1,2)] == (1,2)
nt[1:2] == ???

nt[(:x, :y)] == (1,2)
nt[[:x, :y]] == [1,2]

nt[(a=:x, b=:z)] == (a=1, b=5)
nt[(x=:x, y=:y)] == (x=1, y=3)

# And not this one (because b does not have the indices :x, :y)
nt[(:x, :y)] == (x=1, y=3)

My understanding is that @ararslan is suggesting this:

nt = (x=1, y=3, z=5)
nt[[1,2]] == nt[1:2] == nt[(1,2)] == nt[(:x, :y)] == (x=1, y=3)

# And these are probably errors:
nt[(a=:x, b=:z)]
nt[(x=:x, y=:y)]

vtjnash · 2019-07-25T11:52:46Z

Closes #27021
See also #31423

ararslan · 2019-07-25T14:57:21Z

My understanding is that @ararslan is suggesting this:

nt = (x=1, y=3, z=5)
nt[[1,2]] == nt[1:2] == nt[(1,2)] == nt[(:x, :y)] == (x=1, y=3)

Correct, I am. Though a case could be made to have nt[(:x, :y)] return (1, 3). nt[[:x, :y]] should definitely not be [1, 3] though, c.f. (1, 3)[1:2].

And these are probably errors:

 nt[(a=:x, b=:z)]
 nt[(x=:x, y=:y)]

Yes definitely.

cmcaine · 2019-07-27T23:56:42Z

Latest commit adds tests and implements this behaviour:

nt = (x=1, y=3, z=5)
nt[[1,2]] == nt[1:2] == nt[[1,2]] == nt[[:x, :y]] == (x=1, y=3)

# Indexing with a tuple is an error, as for Tuples.
nt[(1,2)]
nt[(:x, :y)]

# And these are errors:
nt[(a=:x, b=:z)]
nt[(x=:x, y=:y)]

I've removed the fallback method for now.

Fix JuliaLang#32662, JuliaLang#27021

cmcaine · 2019-08-02T13:33:19Z

Is this blocked waiting on a resolution to #30845 or not?

There are now tests and NEWS. I haven't added a compat note in a docstring because there are no getindex docstrings in namedtuple.jl and it's not clear where one should go. The behaviour is basically the same as that already documented for abstract arrays and implemented for arrays and tuples.

mbauman

It's a little annoying, but since Bool <: Integer, we need to also consider the logical indexing case. It's just as easy to support it as disallow it — and as much as it gives me the heeby-geebies, we support it for tuples. So may as well support it here.

Also since you support vectors of Integer, we should probably also support all Integers in the scalar case. I think I got these ad-hoc changes right here.

base/namedtuple.jl

test/namedtuple.jl

mbauman · 2019-08-02T17:32:11Z

I'm not sure where to best put the docs/compat annotation. I guess we could just add a new method-specific docstring for getindex(::NamedTuple, ...) but it's a little funny in that we now just work more like a cross between the two fully-generic behaviors (both dict-like and array-like) that are already documented.

base/namedtuple.jl

cmcaine · 2019-08-02T22:05:23Z

Should we support indexing with LogicalIndex too?

Tuple(1:3)[Base.to_index([true, true, false])] == (1,2)
Tuple(1:3)[Base.to_index([true])] == (1,)

cmcaine · 2019-08-02T22:11:56Z

There's this difference of behaviour between tuple and named tuple when indexing with repeated indices too that I'd like to check everyone is OK with.

julia> (1, 2, 3)[[1,1,1]]
(1, 1, 1)

julia> (x=1, y=-1, z=3)[[1,1]]
(x = 1,)

Co-Authored-By: Matt Bauman <[email protected]>

Co-Authored-By: Jameson Nash <[email protected]>

cmcaine · 2019-08-02T22:30:20Z

I've merged the changes suggested by @mbauman and @vtjnash. Thanks!

cmcaine · 2019-08-20T20:24:32Z

Is there anything outstanding for this to be merged?

vtjnash · 2019-08-20T22:53:18Z

I think the main outstanding question is just whether this now does what anyone expected of it. Beyond the generic map-like or broadcast-like (iteration-based or indexing-based) possibilities for this (or deprecating this entirely for all A[]), this proposes a third option which I’ll call NamedTuple-like as it presents a hybrid interface that seems consistent with the ambiguity in the operation of NT (is it a normal tuple with names added to a side-channel, or should it instead act like a normal set of pairs put in a dict with observable ordering guarantees). Should we put this up for triage and/or vote? Must we we wait for further design proposal and analysis work on A.[] replacement before we can adopt this?

JeffBezanson · 2019-08-29T18:50:40Z

I don't see any examples of compelling use cases for this, and it's not clear how it should work so I think we can wait on this.

mbauman · 2019-08-29T19:10:01Z

As I reconsider this, I'm now against the semantics as they're implemented here and completely agree with Andy's initial comment (#32664 (comment)).

We've found the idiom "the axes of the indices become the axes of the result" to be a very clear and powerful design to help steer these sorts of questions — and this behavior goes against that. So if (x=1,y=2,z=3)[2:3] doesn't return a named tuple, and instead needs returns something with keys matching keys(2:3), should that thing be a vector or a tuple? I say we not worry about this until we either have a clear use-case or an overarching design strategy (e.g., with #30845 and/or #24019).

kescobo · 2023-02-20T23:17:58Z

This PR was linked to from slack just now, and I was confused until I saw how old it is.

I don't think I ever saw this discussion, and it seems like no one that reviewed #38878 did either (or didn't remember it). Perhaps it doesn't actually matter, since that PR only implements getindex on a vector of symbols, but reading this, it seems like maybe there wasn't complete consensus on how this should work, and I'm a bit mortified that it locked in 😬

cmcaine changed the title ~~Allow indexing namedtuples with vectors~~ Support vectors as indices to NamedTuple Jul 24, 2019

cmcaine force-pushed the index-namedtuples branch from 3cdb89f to 6045cff Compare July 24, 2019 00:58

andyferris reviewed Jul 24, 2019

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ararslan added needs compat annotation Add !!! compat "Julia x.y" to the docstring needs news A NEWS entry is required for this change needs tests Unit tests are required for this change labels Jul 24, 2019

cmcaine force-pushed the index-namedtuples branch 2 times, most recently from ac36608 to 598dd41 Compare July 27, 2019 23:56

Support vectors as indices to NamedTuple

aed81fd

Fix JuliaLang#32662, JuliaLang#27021

cmcaine force-pushed the index-namedtuples branch from 598dd41 to aed81fd Compare August 2, 2019 13:32

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Support Bool vectors for indexing NamedTuples

0a528e2

Co-Authored-By: Matt Bauman <[email protected]>

Support [:x,1,2:z] as index to NamedTuple

6945414

Co-Authored-By: Jameson Nash <[email protected]>

cmcaine force-pushed the index-namedtuples branch from 5c6be15 to 6945414 Compare August 2, 2019 22:28

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Support vectors as indices to NamedTuple #32664

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	getindex(t::NamedTuple, v::AbstractVector{Symbol}) = [t[i] for i in v]
	getindex(t::NamedTuple, v::AbstractVector{Symbol}) = (; map(i->i => t[i], t)...)

Support vectors as indices to NamedTuple #32664

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