Let DataLoader(..., batchsize=0) produce one batch

[mcabbott]

Closes #144

Before, treats 0 like "less than 0", perhaps we can call that a bug?

julia> DataLoader([1 2 3; 4 5 6]; batchsize=0)
3-element DataLoader(::Matrix{Int64}, batchsize=0)
  with first element:
  2-element Vector{Int64}

julia> collect(ans)
3-element Vector{Vector{Int64}}:
 [1, 4]
 [2, 5]
 [3, 6]

help?> DataLoader
search: DataLoader

  DataLoader(data; [batchsize, buffer, collate, parallel, partial, rng, shuffle])
[...]
    •  batchsize: If less than 0, iterates over individual observations. Otherwise, each
       iteration (except possibly the last) yields a mini-batch containing batchsize
       observations. Default 1.
[...]

julia> BatchView(1:10, batchsize=0) |> collect
ERROR: DivideError: integer division error

After, converts 0 to numobs on construction:

julia> DataLoader([1 2 3; 4 5 6]; batchsize=0)
1-element DataLoader(::Matrix{Int64}, batchsize=3)
  with first element:
  2×3 Matrix{Int64}

julia> BatchView(1:10, batchsize=0) |> collect  # unchanged
ERROR: DivideError: integer division error

Needs tests, but locally, tests passed with this change. That's some evidence that the zero wasn't really an intentional feature. (In addition to the doc saying "If less than 0".)

[codecov-commenter]

Codecov Report

Merging #145 (fecc37c) into main (ff2fcc1) will increase coverage by 0.32%.
The diff coverage is 100.00%.

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@@            Coverage Diff             @@
##             main     #145      +/-   ##
==========================================
+ Coverage   88.28%   88.60%   +0.32%     
==========================================
  Files          15       13       -2     
  Lines         589      588       -1     
==========================================
+ Hits          520      521       +1     
+ Misses         69       67       -2     

Impacted Files	Coverage Δ
src/eachobs.jl	87.35% <100.00%> (+0.14%)	⬆️
src/Datasets/Datasets.jl
src/MLUtils.jl

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[CarloLucibello]

Before, treats 0 like "less than 0", perhaps we can call that a bug?

yes, doesn't deserve a major version bump

[CarloLucibello]

well actually previous batchsize=0 behavior is useful, disables batching and makes the dataloader equivalent to eachobs, something that cannot be obtained with batchsize=1.
Maybe we can set batchsize=nothing for maximum batch size?

[mcabbott]

equivalent to eachobs, something that cannot be obtained with batchsize=1

Isn't this batchsize=-1? That's what the docs seem to say:

julia> DataLoader(ones(2,3); batchsize=1) |> first
2×1 Matrix{Float64}:
 1.0
 1.0

julia> DataLoader(ones(2,3); batchsize=-1) |> first
2-element Vector{Float64}:
 1.0
 1.0

julia> eachobs(ones(2,3)) |> first
2-element Vector{Float64}:
 1.0
 1.0

[mcabbott]

Perhaps ideally, batchsize=0 would make more sense for the "individual obs without batch dim" command, and batchsize=-1 for "wrap around to largest possible batch". Both are special cases. But this way around would clearly break documented behaviour.

My first idea in #144 was to use batchsize=Inf for "largest possible". It's a little weird to allow only one Float64 value.

Are there other good tokens? Using a function like batchsize=all seems clear to read but pretty unusual. Base uses dims=: internally in many places for "all the dimensions", but not quite like this; seems more like sum(rand(2,3); dims=(1,2))::Matrix than like sum(rand(2,3); dims=:)::Number.