4.10.4 Using a Vertex Set to Create a Bipartite Subgraph

You can create a bipartite subgraph by specifying a set of vertices (nodes), which are used as the left side. A bipartite subgraph has edges only between the left set of vertices and the right set of vertices. There are no edges within those sets, such as between two nodes on the left side. In the in-memory graph server (PGX), vertices that are isolated because all incoming and outgoing edges were deleted are not part of the bipartite subgraph.

The following figure shows a bipartite subgraph. No properties are shown.

Description of the illustration pgx_bipartite_graph.png

The following examples create a bipartite subgraph from a simple graph consisting of four vertices and four edges. The vertex ID values for the four vertices are 99, 128, 1908 and 333 respectively. See Figure 4-5 in About Filter Expressions for more information on the vertex and edge property values including the edge direction between the vertices.

You must first create a vertex collection and fill it with the vertices for the left side. In the example shown, vertices with vertex ID values 333 and 99 are added to the left side of the vertex collection.

Using the Shell to Create a Bipartite Subgraph

opg4j> s = graph.createVertexSet()
==> ...
opg4j> s.addAll([graph.getVertex(333), graph.getVertex(99)])
==> ...
opg4j> s.size()
==> 2
opg4j> bGraph = graph.bipartiteSubGraphFromLeftSet(s)
==> PGX Bipartite Graph named sample-sub-graph-4

Using Java to Create a Bipartite Subgraph

import oracle.pgx.api.*;
 
VertexSet<Integer> s = graph.createVertexSet();
s.addAll(graph.getVertex(333), graph.getVertex(99));
BipartiteGraph bGraph = graph.bipartiteSubGraphFromLeftSet(s);

When you create a subgraph, the in-memory graph server (PGX) automatically creates a Boolean vertex (node) property that indicates whether the vertex is on the left side. You can specify a unique name for the property.

The resulting bipartite subgraph looks like this:

Description of the illustration pgx_bipartite_subgraph.png

Vertex with ID 1908 is excluded from the bipartite subgraph. The only edge that connected that vertex extended from 128 to 1908. The edge was removed, because it violated the bipartite properties of the subgraph. Vertex 1908 had no other edges, and so was removed as well. Moreover, the edge from the vertex with the ID 128 to the vertex with ID 99 is not present in the bipartite subgraph, because edges are only allowed to go from left to right (and not from right to left).