Implementing an iterator that goes through the pixels in the torch mnist dataset

pixel_iterator_on_torch_mnist.lua

train = torch.load('mnist.t7/train_32x32.t7', 'ascii')
train.data = train.data:type(torch.getdefaulttensortype())

function pixels(dataset)
    local dimensions = (#dataset.data):totable()    
    local data = dataset.data
    local d1 = 1
    local d2 = 1
    local d3 = 1
    local d4 = 1
    return function()
        while (d1 <= dimensions[1]) do
            while (d2 <= dimensions[2]) do
                while (d3 <= dimensions[3]) do
                    while (d4 <= dimensions[4]) do
                        cur = data[d1][d2][d3][d4]
                        d4 = d4 + 1
                        return cur
                    end
                    d3 = d3 + 1
                    d4 = 1
                end
                d2 = d2 + 1
                d3 = 1
            end
            d1 = d1 + 1
            d2 = 1
        end
    end
end
       
sum = 0
for pixel in pixels(train) do    
    sum = sum + pixel
end

print(sum)
print(train.data:sum())