Add script to download and prepare MNIST #1

Data/get_mnist.m

@@ -0,0 +1,60 @@
+% Download and prepare MNIST
+
+%% Download
+files = {'train-images-idx3-ubyte', 'train-labels-idx1-ubyte', ...
+         't10k-images-idx3-ubyte', 't10k-labels-idx1-ubyte'};
+for i = 1:numel(files)
+   if ~exist(files{i}, 'file')
+       url = ['http://yann.lecun.com/exdb/mnist/', files{i}, '.gz'];
+       disp(['Downloading ', url]);
+       gunzip(url);
+       assert(exist(files{i}, 'file') == 2, ['Could not download ', files{i}]);
+   end
+end
+
+%% Read Images
+files = {'train-images-idx3-ubyte', 't10k-images-idx3-ubyte'};
+for i = 1:numel(files)
+    f = fopen(files{i}, 'rb');
+    assert(f ~= -1, ['Could not open ', files{i}]);
+
+    magic = fread(f, 1, 'int32', 0, 'ieee-be');
+    assert(magic == 2051, ['Bad magic number in ', files{i}]);
+
+    numImages = fread(f, 1, 'int32', 0, 'ieee-be');
+    numRows = fread(f, 1, 'int32', 0, 'ieee-be');
+    numCols = fread(f, 1, 'int32', 0, 'ieee-be');
+
+    X{i} = fread(f, inf, 'unsigned char');
+    X{i} = reshape(X{i}, numCols, numRows, numImages);
+    X{i} = permute(X{i},[3 2 1]);
+    X{i} = reshape(X{i}, size(X{i}, 1), size(X{i}, 2) * size(X{i}, 3));
+
+    fclose(f); 
+end
+
+%% Read Labels
+files = {'train-labels-idx1-ubyte', 't10k-labels-idx1-ubyte'};
+for i = 1:numel(files)
+    f = fopen(files{i}, 'rb');
+    assert(f ~= -1, ['Could not open ', files{i}]);
+
+    magic = fread(f, 1, 'int32', 0, 'ieee-be');
+    assert(magic == 2049, ['Bad magic number in ', files{i}]);
+
+    numLabels = fread(f, 1, 'int32', 0, 'ieee-be');
+
+    Y{i} = fread(f, inf, 'unsigned char');
+    assert(size(Y{i},1) == numLabels, 'Mismatch in label count');
+
+    fclose(f);
+end
+
+%% Prepare & Save
+train_x = uint8(X{1});
+train_y = uint8(dummyvar(Y{1} + 1));
+test_x = uint8(X{2});
+test_y = uint8(dummyvar(Y{2} + 1));
+assert(size(train_x, 1) == size(train_y, 1), 'Mismatch in training set');
+assert(size(test_x, 1) == size(test_y, 1), 'Mismatch in test set');
+save -v7.3 mnist_uint8 train_x train_y test_x test_y;