Add the ability to check bipartiteness of directed and undirected

xgi/convert/bipartite_graph.py

@@ -1,11 +1,11 @@
 """Methods for converting to and from bipartite graphs."""
 
 import networkx as nx
+
 import xgi
-from networkx import bipartite
 
 from ..exception import XGIError
-from ..generators import empty_hypergraph, empty_dihypergraph
+from ..generators import empty_dihypergraph, empty_hypergraph
 
 __all__ = ["from_bipartite_graph", "to_bipartite_graph"]
 
@@ -74,12 +74,12 @@ def from_bipartite_graph(G, create_using=None, dual=False):
         else:
             raise XGIError("Invalid type specifier")
 
+    if not _is_bipartite(G, nodes, edges):
+        raise XGIError("The network is not bipartite")
+
     if G.is_directed():
         H = empty_dihypergraph(create_using)
     else:
-        if not bipartite.is_bipartite_node_set(G, nodes):
-            raise XGIError("The network is not bipartite")
-
         H = empty_hypergraph(create_using)
 
     H.add_nodes_from(nodes)
@@ -95,6 +95,16 @@ def from_bipartite_graph(G, create_using=None, dual=False):
     return H.dual() if dual else H
 
 
+def _is_bipartite(G, nodes1, nodes2):
+    """Assumption is that nodes1.union(nodes2) == G.nodes"""
+    for i, j in G.edges:
+        cond1 = i in nodes1
+        cond2 = j in nodes2
+        if not cond1 == cond2:  # if not both true or both false
+            return False
+    return True
+
+
 def to_bipartite_graph(H, index=False):
     """Create a NetworkX bipartite network from a hypergraph.