Usps dataset (#961)

* add USPS dataset

* minor fixes

* Improvements to the USPS dataset

Add it to the documentation, expose it to torchvision.datasets
and inherit from VisionDataset

docs/source/datasets.rst

@@ -188,3 +188,10 @@ SBD
 .. autoclass:: SBDataset
   :members: __getitem__
   :special-members:
+
+USPS
+~~~~~
+
+.. autoclass:: USPS
+  :members: __getitem__
+  :special-members:

torchvision/datasets/__init__.py

@@ -18,6 +18,7 @@
 from .celeba import CelebA
 from .sbd import SBDataset
 from .vision import VisionDataset
+from .usps import USPS
 
 __all__ = ('LSUN', 'LSUNClass',
            'ImageFolder', 'DatasetFolder', 'FakeData',
@@ -26,4 +27,5 @@
            'MNIST', 'KMNIST', 'STL10', 'SVHN', 'PhotoTour', 'SEMEION',
            'Omniglot', 'SBU', 'Flickr8k', 'Flickr30k',
            'VOCSegmentation', 'VOCDetection', 'Cityscapes', 'ImageNet',
-           'Caltech101', 'Caltech256', 'CelebA', 'SBDataset', 'VisionDataset')
+           'Caltech101', 'Caltech256', 'CelebA', 'SBDataset', 'VisionDataset',
+           'USPS')

torchvision/datasets/usps.py

@@ -0,0 +1,83 @@
+from __future__ import print_function
+from PIL import Image
+import os
+import numpy as np
+
+from .utils import download_url
+from .vision import VisionDataset
+
+
+class USPS(VisionDataset):
+    """`USPS <https://www.csie.ntu.edu.tw/~cjlin/libsvmtools/datasets/multiclass.html#usps>`_ Dataset.
+    The data-format is : [label [index:value ]*256 \n] * num_lines, where ``label`` lies in ``[1, 10]``.
+    The value for each pixel lies in ``[-1, 1]``. Here we transform the ``label`` into ``[0, 9]``
+    and make pixel values in ``[0, 255]``.
+
+    Args:
+        root (string): Root directory of dataset to store``USPS`` data files.
+        train (bool, optional): If True, creates dataset from ``usps.bz2``,
+            otherwise from ``usps.t.bz2``.
+        transform (callable, optional): A function/transform that  takes in an PIL image
+            and returns a transformed version. E.g, ``transforms.RandomCrop``
+        target_transform (callable, optional): A function/transform that takes in the
+            target and transforms it.
+        download (bool, optional): If true, downloads the dataset from the internet and
+            puts it in root directory. If dataset is already downloaded, it is not
+            downloaded again.
+
+    """
+    split_list = {
+        'train': [
+            "https://www.csie.ntu.edu.tw/~cjlin/libsvmtools/datasets/multiclass/usps.bz2",
+            "usps.bz2", 'ec16c51db3855ca6c91edd34d0e9b197'
+        ],
+        'test': [
+            "https://www.csie.ntu.edu.tw/~cjlin/libsvmtools/datasets/multiclass/usps.t.bz2",
+            "usps.t.bz2", '8ea070ee2aca1ac39742fdd1ef5ed118'
+        ],
+    }
+
+    def __init__(self, root, train=True, transform=None, target_transform=None, download=False):
+        super(USPS, self).__init__(root, transform=transform, target_transform=target_transform)
+        split = 'train' if train else 'test'
+        url, filename, checksum = self.split_list[split]
+        full_path = os.path.join(self.root, filename)
+
+        if download and not os.path.exists(full_path):
+            download_url(url, self.root, filename, md5=checksum)
+
+        import bz2
+        with bz2.open(full_path) as fp:
+            raw_data = [l.decode().split() for l in fp.readlines()]
+            imgs = [[x.split(':')[-1] for x in data[1:]] for data in raw_data]
+            imgs = np.asarray(imgs, dtype=np.float32).reshape((-1, 16, 16))
+            imgs = ((imgs + 1) / 2 * 255).astype(dtype=np.uint8)
+            targets = [int(d[0]) - 1 for d in raw_data]
+
+        self.data = imgs
+        self.targets = targets
+
+    def __getitem__(self, index):
+        """
+        Args:
+            index (int): Index
+
+        Returns:
+            tuple: (image, target) where target is index of the target class.
+        """
+        img, target = self.data[index], int(self.targets[index])
+
+        # doing this so that it is consistent with all other datasets
+        # to return a PIL Image
+        img = Image.fromarray(img, mode='L')
+
+        if self.transform is not None:
+            img = self.transform(img)
+
+        if self.target_transform is not None:
+            target = self.target_transform(target)
+
+        return img, target
+
+    def __len__(self):
+        return len(self.data)