extend dataloader

src/data/dataloader.jl

@@ -12,13 +12,14 @@ end
 
 """
     DataLoader(data...; batchsize=1, shuffle=false, partial=true)
+    DataLoader(data::Tuple; ...)
 
 An object that iterates over mini-batches of `data`, each mini-batch containing `batchsize` observations
 (except possibly the last one). 
 
-Takes as input one or more data tensors, e.g. X in unsupervised learning, X and Y in 
-supervised learning. The last dimension in each tensor is considered to be the observation
-dimension. 
+Takes as input one or more data tensors (e.g. X in unsupervised learning, X and Y in 
+supervised learning,) or a tuple of such tensors. 
+The last dimension in each tensor is considered to be the observation dimension. 
 
 If `shuffle=true`, shuffles the observations each time iterations are re-started.
 If `partial=false`, drops the last mini-batch if it is smaller than the batchsize.
@@ -35,11 +36,27 @@ Example usage:
         ...
     end
 
+    train_loader = DataLoader(Xtrain, batchsize=2) 
+    # iterate over 50 mini-batches of size 2
+    for x in train_loader
+        @assert size(x) == (10, 2)
+        ...
+    end
+
     train_loader.data   # original dataset
 
+    # similar but yelding tuples
+    train_loader = DataLoader((Xtrain,), batchsize=2) 
+    for (x,) in train_loader
+        @assert size(x) == (10, 2)
+        ...
+    end
+
     Xtrain = rand(10, 100)
     Ytrain = rand(100)
     train_loader = DataLoader(Xtrain, Ytrain, batchsize=2, shuffle=true) 
+    # or equivalently
+    train_loader = DataLoader((Xtrain, Ytrain), batchsize=2, shuffle=true) 
     for epoch in 1:100
         for (x, y) in train_loader
             @assert size(x) == (10, 2)
@@ -52,24 +69,20 @@ Example usage:
     using IterTools: ncycle 
     Flux.train!(loss, ps, ncycle(train_loader, 10), opt)
 """
-function DataLoader(data...; batchsize=1, shuffle=false, partial=true)
-    length(data) > 0 || throw(ArgumentError("Need at least one data input"))
+function DataLoader(data; batchsize=1, shuffle=false, partial=true)
     batchsize > 0 || throw(ArgumentError("Need positive batchsize"))
     
-    nx = size(data[1])[end]
-    for i=2:length(data)
-        nx != size(data[i])[end] && throw(DimensionMismatch("All data should contain same number of observations"))
+    n = _nobs(data) 
+    if n < batchsize
+        @warn "Number of observations less than batchsize, decreasing the batchsize to $n"
+        batchsize = n
     end
-    if nx < batchsize
-        @warn "Number of data points less than batchsize, decreasing the batchsize to $nx"
-        batchsize = nx
-    end
-    imax = partial ? nx : nx - batchsize + 1
-    ids = 1:min(nx, batchsize)
-    DataLoader(data, batchsize, nx, partial, imax, [1:nx;], shuffle)
+    imax = partial ? n : n - batchsize + 1
+    ids = 1:min(n, batchsize)
+    DataLoader(data, batchsize, n, partial, imax, [1:n;], shuffle)
 end
 
-getdata(x::AbstractArray, ids) = x[(Base.Colon() for _=1:ndims(x)-1)..., ids]
+DataLoader(data...; kws...) = DataLoader(data; kws...)
 
 @propagate_inbounds function Base.iterate(d::DataLoader, i=0)     # returns data in d.indices[i+1:i+batchsize]
     i >= d.imax && return nothing
@@ -78,11 +91,7 @@ getdata(x::AbstractArray, ids) = x[(Base.Colon() for _=1:ndims(x)-1)..., ids]
     end
     nexti = min(i + d.batchsize, d.nobs)
     ids = d.indices[i+1:nexti]
-    if length(d.data) == 1
-        batch = getdata(d.data[1], ids)
-    else
-        batch = ((getdata(x, ids) for x in d.data)...,)
-    end
+    batch = _getobs(d.data, ids)
     return (batch, nexti)
 end
 
@@ -90,3 +99,17 @@ function Base.length(d::DataLoader)
     n = d.nobs / d.batchsize
     d.partial ? ceil(Int,n) : floor(Int,n)
 end
+
+_nobs(data::AbstractArray) = size(data)[end]
+
+function _nobs(data::Tuple)
+    length(data) > 0 || throw(ArgumentError("Need at least one data input"))
+    n = _nobs(data[1])
+    if !all(x -> _nobs(x) == n, data[2:end])
+        throw(DimensionMismatch("All data should contain same number of observations"))
+    end
+    return n
+end
+
+_getobs(data::AbstractArray, i) = data[(Base.Colon() for _=1:ndims(data)-1)..., i]
+_getobs(data::Tuple, i) = ((_getobs(x, i) for x in data)...,)