[Dataset] RedditDataset change data.train_mask to numpy array (#1961)

* PPIDataset

* Revert "PPIDataset"

This reverts commit 264bd0c960cfa698a7bb946dad132bf52c2d0c8a.

* Update reddit.py
Co-authored-by: xiang song(charlie.song) <classicxsong@gmail.com>

python/dgl/data/reddit.py

@@ -94,11 +94,11 @@ class RedditDataset(DGLBuiltinDataset):
         Graph of the dataset
     num_labels : int
         Number of classes for each node
-    train_mask: Tensor
+    train_mask: numpy.ndarray
         Mask of training nodes
-    val_mask: Tensor
+    val_mask: numpy.ndarray
         Mask of validation nodes
-    test_mask: Tensor
+    test_mask: numpy.ndarray
         Mask of test nodes
     features : Tensor
         Node features
@@ -202,17 +202,17 @@ class RedditDataset(DGLBuiltinDataset):
     @property
     def train_mask(self):
         deprecate_property('dataset.train_mask', 'graph.ndata[\'train_mask\']')
-        return self._graph.ndata['train_mask']
+        return F.asnumpy(self._graph.ndata['train_mask'])
 
     @property
     def val_mask(self):
         deprecate_property('dataset.val_mask', 'graph.ndata[\'val_mask\']')
-        return self._graph.ndata['val_mask']
+        return F.asnumpy(self._graph.ndata['val_mask'])
 
     @property
     def test_mask(self):
         deprecate_property('dataset.test_mask', 'graph.ndata[\'test_mask\']')
-        return self._graph.ndata['test_mask']
+        return F.asnumpy(self._graph.ndata['test_mask'])
 
     @property
     def features(self):