[Dataset] KarateClubDataset (#1897)

* karateclub dataset

* PPIDataset

* Revert "PPIDataset"

This reverts commit 264bd0c960cfa698a7bb946dad132bf52c2d0c8a.

* Update karate.py

* doc string
Co-authored-by: xiang song(charlie.song) <classicxsong@gmail.com>

python/dgl/data/__init__.py

@@ -11,12 +11,13 @@ from .reddit import RedditDataset
 from .ppi import PPIDataset, LegacyPPIDataset
 from .tu import TUDataset, LegacyTUDataset
 from .gnn_benckmark import AmazonCoBuy, CoraFull, Coauthor
-from .karate import KarateClub
+from .karate import KarateClub, KarateClubDataset
 from .gindt import GINDataset
 from .bitcoinotc import BitcoinOTC
 from .gdelt import GDELT
 from .icews18 import ICEWS18
 from .qm7b import QM7b
+from .dgl_dataset import DGLDataset, DGLBuiltinDataset
 from .citation_graph import CoraGraphDataset, CiteseerGraphDataset, PubmedGraphDataset
 
 

python/dgl/data/karate.py

@@ -2,30 +2,92 @@
 """
 import numpy as np
 import networkx as nx
-from .. import convert
 
+from .. import backend as F
+from .dgl_dataset import DGLDataset
+from .utils import deprecate_property
+from ..convert import graph as dgl_graph
 
-class KarateClub(object):
-    """
-    Zachary's karate club is a social network of a university karate club, described in the paper
-    "An Information Flow Model for Conflict and Fission in Small Groups" by Wayne W. Zachary. The
-    network became a popular example of community structure in networks after its use by Michelle
-    Girvan and Mark Newman in 2002.
+__all__ = ['KarateClubDataset', 'KarateClub']
 
-    This dataset has only one graph, with ndata 'label' means whether the node is belong to the "Mr. Hi" club.
-    """
 
+class KarateClubDataset(DGLDataset):
+    r""" Karate Club dataset for Node Classification
+
+    .. deprecated:: 0.5.0
+        `data` is deprecated, it is replaced by:
+            >>> dataset = KarateClubDataset()
+            >>> g = dataset[0]
+
+    Zachary's karate club is a social network of a university
+    karate club, described in the paper "An Information Flow
+    Model for Conflict and Fission in Small Groups" by Wayne W. Zachary.
+    The network became a popular example of community structure in
+    networks after its use by Michelle Girvan and Mark Newman in 2002.
+    Official website: http://konect.cc/networks/ucidata-zachary/
+
+    Karate Club dataset statistics:
+    Nodes: 34
+    Edges: 156
+    Number of Classes: 2
+
+    Attributes
+    ----------
+    num_classes : int
+        Number of node classes
+    data : list
+        A list of DGLGraph objects
+
+    Examples
+    --------
+    >>> dataset = KarateClubDataset()
+    >>> num_classes = dataset.num_classes
+    >>> g = dataset[0]
+    >>> labels = g.ndata['label']
+    """
     def __init__(self):
-        kG = nx.karate_club_graph()
-        self.label = np.asarray(
-            [kG.nodes[i]['club'] != 'Mr. Hi' for i in kG.nodes]).astype(np.int64)
-        g = convert.graph(kG)
-        g.ndata['label'] = self.label
-        self.data = [g]
+        super(KarateClubDataset, self).__init__(name='karate_club')
+
+    def process(self):
+        kc_graph = nx.karate_club_graph()
+        label = np.asarray(
+            [kc_graph.nodes[i]['club'] != 'Mr. Hi' for i in kc_graph.nodes]).astype(np.int64)
+        label = F.tensor(label)
+        g = dgl_graph(kc_graph)
+        g.ndata['label'] = label
+        self._graph = g
+        self._data = [g]
+
+    @property
+    def num_classes(self):
+        """Number of classes."""
+        return 2
+
+    @property
+    def data(self):
+        deprecate_property('dataset.data', 'dataset[0]')
+        return self._data
 
     def __getitem__(self, idx):
+        r""" Get graph object
+
+        Parameters
+        ----------
+        idx : int
+            Item index, KarateClubDataset has only one graph object
+
+        Returns
+        -------
+        dgl.DGLGraph
+            graph structure and labels.
+            - ndata['label']: ground truth labels
+        """
         assert idx == 0, "This dataset has only one graph"
-        return self.data[0]
+        return self._graph
 
     def __len__(self):
-        return len(self.data)
+        r"""The number of graphs in the dataset."""
+        return 1
+
+
+KarateClub = KarateClubDataset