node/edge filtering (dmlc#80)

* node/edge filtering

* changing to tensor operations (what did i do???)

* ???

python/dgl/backend/numpy.py

@@ -22,3 +22,7 @@ def unpack(a, split_size_or_sections=None):
 
 def shape(a):
     return a.shape
+
+def nonzero_1d(a):
+    assert a.ndim == 2
+    return np.nonzero(a)[0]

python/dgl/backend/pytorch.py

@@ -143,3 +143,8 @@ def zerocopy_from_numpy(np_data):
     arr.ctx = get_context(data)
     return arr
     '''
+
+def nonzero_1d(arr):
+    """Return a 1D tensor with nonzero element indices in a 1D vector"""
+    assert arr.dim() == 1
+    return th.nonzero(arr)[:, 0]

python/dgl/graph.py

@@ -3,6 +3,7 @@
 from __future__ import absolute_import
 
 import networkx as nx
+import numpy as np
 
 import dgl
 from .base import ALL, is_all, __MSG__, __REPR__
@@ -1285,3 +1286,57 @@ def line_graph(self, backtracking=True, shared=False):
         graph_data = self._graph.line_graph(backtracking)
         node_frame = self._edge_frame if shared else None
         return DGLGraph(graph_data, node_frame)
+
+    def filter_nodes(self, predicate, nodes=ALL):
+        """Return a tensor of node IDs that satisfy the given predicate.
+
+        Parameters
+        ----------
+        predicate : callable
+            The predicate should take in a dict of tensors whose values
+            are concatenation of node representations by node ID (same as
+            get_n_repr()), and return a boolean tensor with N elements
+            indicating which node satisfy the predicate.
+        nodes : container or tensor
+            The nodes to filter on
+
+        Returns
+        -------
+        tensor
+            The filtered nodes
+        """
+        n_repr = self.get_n_repr(nodes)
+        n_mask = predicate(n_repr)
+
+        if is_all(nodes):
+            return F.nonzero_1d(n_mask)
+        else:
+            nodes = F.Tensor(nodes)
+            return nodes[n_mask]
+
+    def filter_edges(self, predicate, edges=ALL):
+        """Return a tensor of edge IDs that satisfy the given predicate.
+
+        Parameters
+        ----------
+        predicate : callable
+            The predicate should take in a dict of tensors whose values
+            are concatenation of edge representations by edge ID (same as
+            get_e_repr_by_id()), and return a boolean tensor with N elements
+            indicating which node satisfy the predicate.
+        edges : container or tensor
+            The edges to filter on
+
+        Returns
+        -------
+        tensor
+            The filtered edges
+        """
+        e_repr = self.get_e_repr_by_id(edges)
+        e_mask = predicate(e_repr)
+
+        if is_all(edges):
+            return F.nonzero_1d(e_mask)
+        else:
+            edges = F.Tensor(edges)
+            return edges[e_mask]

tests/pytorch/test_filter.py

@@ -0,0 +1,39 @@
+import torch as th
+import numpy as np
+from dgl.graph import DGLGraph
+
+def test_filter():
+    g = DGLGraph()
+    g.add_nodes(4)
+    g.add_edges([0,1,2,3], [1,2,3,0])
+
+    n_repr = th.zeros(4, 5)
+    e_repr = th.zeros(4, 5)
+    n_repr[[1, 3]] = 1
+    e_repr[[1, 3]] = 1
+
+    g.set_n_repr({'a': n_repr})
+    g.set_e_repr({'a': e_repr})
+
+    def predicate(r):
+        return r['a'].max(1)[0] > 0
+
+    # full node filter
+    n_idx = g.filter_nodes(predicate)
+    assert set(n_idx.numpy()) == {1, 3}
+
+    # partial node filter
+    n_idx = g.filter_nodes(predicate, [0, 1])
+    assert set(n_idx.numpy()) == {1}
+
+    # full edge filter
+    e_idx = g.filter_edges(predicate)
+    assert set(e_idx.numpy()) == {1, 3}
+
+    # partial edge filter
+    e_idx = g.filter_edges(predicate, [0, 1])
+    assert set(e_idx.numpy()) == {1}
+
+
+if __name__ == '__main__':
+    test_filter()