"""
eachobs(data; kws...)
Return an iterator over `data`.
Supports the same arguments as [`DataLoader`](@ref).
The `batchsize` default is `-1` here while
it is `1` for `DataLoader`.
# Examples
```julia
X = rand(4,100)
for x in eachobs(X)
# loop entered 100 times
@assert typeof(x) <: Vector{Float64}
@assert size(x) == (4,)
end
# mini-batch iterations
for x in eachobs(X, batchsize=10)
# loop entered 10 times
@assert typeof(x) <: Matrix{Float64}
@assert size(x) == (4,10)
end
# support for tuples, named tuples, dicts
for (x, y) in eachobs((X, Y))
# ...
end
```
"""
function
eachobs
(
data
;
batchsize
=
-1
,
kws
...
)
DataLoader
(
data
;
batchsize
,
kws
...
)
end
"""
DataLoader(data; [batchsize, buffer, collate, parallel, partial, rng, shuffle])
An object that iterates over mini-batches of `data`,
each mini-batch containing `batchsize` observations
(except possibly the last one).
Takes as input a single data array, a tuple (or a named tuple) of arrays,
or in general any `data` object that implements the [`numobs`](@ref) and [`getobs`](@ref)
methods.
The last dimension in each array is the observation dimension, i.e. the one
divided into mini-batches.
The original data is preserved in the `data` field of the DataLoader.
# Arguments
- `data`: The data to be iterated over. The data type has to be supported by
[`numobs`](@ref) and [`getobs`](@ref).
- `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`.
- `buffer`: If `buffer=true` and supported by the type of `data`,
a buffer will be allocated and reused for memory efficiency.
You can also pass a preallocated object to `buffer`. Default `false`.
- `collate`: Batching behavior. If `nothing` (default), a batch is `getobs(data, indices)`. If `false`, each batch is
`[getobs(data, i) for i in indices]`. When `true`, applies [`batch`](@ref) to the vector of observations in a batch,
recursively collating arrays in the last dimensions. See [`batch`](@ref) for more information and examples.
- `parallel`: Whether to use load data in parallel using worker threads. Greatly
speeds up data loading by factor of available threads. Requires starting
Julia with multiple threads. Check `Threads.nthreads()` to see the number of
available threads. **Passing `parallel = true` breaks ordering guarantees**.
Default `false`.
- `partial`: This argument is used only when `batchsize > 0`.
If `partial=false` and the number of observations is not divisible by the batchsize,
then the last mini-batch is dropped. Default `true`.
- `rng`: A random number generator. Default `Random.GLOBAL_RNG`.
- `shuffle`: Whether to shuffle the observations before iterating. Unlike
wrapping the data container with `shuffleobs(data)`, `shuffle=true` ensures
that the observations are shuffled anew every time you start iterating over
`eachobs`. Default `false`.
# Examples
```jldoctest
julia> Xtrain = rand(10, 100);
julia> array_loader = DataLoader(Xtrain, batchsize=2);
julia> for x in array_loader
@assert size(x) == (10, 2)
# do something with x, 50 times
end
julia> array_loader.data === Xtrain
true
julia> tuple_loader = DataLoader((Xtrain,), batchsize=2); # similar, but yielding 1-element tuples
julia> for x in tuple_loader
@assert x isa Tuple{Matrix}
@assert size(x[1]) == (10, 2)
end
julia> Ytrain = rand('a':'z', 100); # now make a DataLoader yielding 2-element named tuples
julia> train_loader = DataLoader((data=Xtrain, label=Ytrain), batchsize=5, shuffle=true);
julia> for epoch in 1:100
for (x, y) in train_loader # access via tuple destructuring
@assert size(x) == (10, 5)
@assert size(y) == (5,)
# loss += f(x, y) # etc, runs 100 * 20 times
end
end
julia> first(train_loader).label isa Vector{Char} # access via property name
true
julia> first(train_loader).label == Ytrain[1:5] # because of shuffle=true
false
julia> foreach(println∘summary, DataLoader(rand(Int8, 10, 64), batchsize=30)) # partial=false would omit last
10×30 Matrix{Int8}
10×30 Matrix{Int8}
10×4 Matrix{Int8}
```
"""
struct
DataLoader
{
T
,
R
<:
AbstractRNG
,
C
<:
Val
}
data
::
T
batchsize
::
Int
buffer
::
Bool
partial
::
Bool
shuffle
::
Bool
parallel
::
Bool
collate
::
C
rng
::
R
end
function
DataLoader
(
data
;
buffer
=
false
,
parallel
=
false
,
shuffle
=
false
,
batchsize
::
Int
=
1
,
partial
::
Bool
=
true
,
collate
=
Val
(
nothing
)
,
rng
::
AbstractRNG
=
Random
.
GLOBAL_RNG
)
buffer
=
buffer
isa
Bool
?
buffer
:
true
collate
=
collate
isa
Val
?
collate
:
Val
(
collate
)
if
!
(
collate
∈
(
Val
(
nothing
)
,
Val
(
true
)
,
Val
(
false
)
)
)
throw
(
ArgumentError
(
"
`collate` must be one of `nothing`, `true` or `false`.
"
)
)
end
return
DataLoader
(
data
,
batchsize
,
buffer
,
partial
,
shuffle
,
parallel
,
collate
,
rng
)
end
function
Base
.
iterate
(
e
::
DataLoader
)
data
=
ObsView
(
e
.
data
)
data
=
e
.
shuffle
?
shuffleobs
(
e
.
rng
,
data
)
:
data
data
=
e
.
batchsize
>
0
?
BatchView
(
data
;
e
.
batchsize
,
e
.
partial
,
e
.
collate
)
:
data
iter
=
if
e
.
parallel
eachobsparallel
(
data
;
e
.
buffer
)
else
if
e
.
buffer
buf
=
getobs
(
data
,
1
)
(
getobs!
(
buf
,
data
,
i
)
for
i
in
1
:
numobs
(
data
)
)
else
(
getobs
(
data
,
i
)
for
i
in
1
:
numobs
(
data
)
)
end
end
obs
,
state
=
iterate
(
iter
)
return
obs
,
(
iter
,
state
)
end
function
Base
.
iterate
(
::
DataLoader
,
(
iter
,
state
)
)
ret
=
iterate
(
iter
,
state
)
isnothing
(
ret
)
&&
return
obs
,
state
=
ret
return
obs
,
(
iter
,
state
)
end
function
Base
.
length
(
e
::
DataLoader
)
numobs
(
if
e
.
batchsize
>
0
data
=
ObsView
(
e
.
data
)
BatchView
(
data
;
e
.
batchsize
,
e
.
partial
)
else
e
.
data
end
)
end
Base
.
IteratorEltype
(
::
DataLoader
)
=
Base
.
EltypeUnknown
(
)
This causes error in some cases of
collect(loader) function Base.eltype(e::DataLoader) eltype(if e.batchsize > 0 BatchView(e.data; e.batchsize, e.partial) else e.data end) end
@
inline
function
_dataloader_foldl1
(
rf
,
val
,
e
::
DataLoader
,
data
)
if
e
.
shuffle
_dataloader_foldl2
(
rf
,
val
,
e
,
shuffleobs
(
e
.
rng
,
data
)
)
else
_dataloader_foldl2
(
rf
,
val
,
e
,
data
)
end
end
@
inline
function
_dataloader_foldl2
(
rf
,
val
,
e
::
DataLoader
,
data
)
if
e
.
batchsize
>
0
_dataloader_foldl3
(
rf
,
val
,
e
,
BatchView
(
data
;
e
.
batchsize
,
e
.
partial
)
)
else
_dataloader_foldl3
(
rf
,
val
,
e
,
data
)
end
end
@
inline
function
_dataloader_foldl3
(
rf
,
val
,
e
::
DataLoader
,
data
)
if
e
.
buffer
>
0
_dataloader_foldl4_buffered
(
rf
,
val
,
data
)
else
_dataloader_foldl4
(
rf
,
val
,
data
)
end
end
@
inline
function
_dataloader_foldl4
(
rf
,
val
,
data
)
for
i
in
1
:
numobs
(
data
)
@
inbounds
x
=
getobs
(
data
,
i
)
val
=
Transducers
.
@
next
(
rf
,
val
,
x
)
end
Transducers
.
complete
(
rf
,
val
)
end
@
inline
function
_dataloader_foldl4_buffered
(
rf
,
val
,
data
)
buf
=
getobs
(
data
,
1
)
for
i
in
1
:
numobs
(
data
)
@
inbounds
x
=
getobs!
(
buf
,
data
,
i
)
val
=
Transducers
.
@
next
(
rf
,
val
,
x
)
end
Transducers
.
complete
(
rf
,
val
)
end
@
inline
function
Transducers
.
__foldl__
(
rf
,
val
,
e
::
DataLoader
)
e
.
parallel
&&
throw
(
ArgumentError
(
"
Transducer fold protocol not supported on parallel data loads
"
)
)
_dataloader_foldl1
(
rf
,
val
,
e
,
ObsView
(
e
.
data
)
)
end