Support DiHypergraph in from_bipartite_graph

tests/conftest.py

@@ -135,6 +135,21 @@ def bipartite_graph4():
     return G
 
 
+@pytest.fixture
+def bipartite_dihypergraph1():
+    G = nx.DiGraph()
+    G.add_nodes_from([1, 2, 3, 4], bipartite=0)
+    G.add_nodes_from(["a", "b", "c"], bipartite=1)
+    G.add_edges_from([
+        ("a", 1),
+        ("b", 1, {"direction": "tail"}),
+        ("b", 2),
+        ("c", 2, {"direction": "tail"}),
+        ("c", 3),
+        ("a", 4, {"direction": "tail"})])
+    return G
+
+
 @pytest.fixture
 def attr0():
     return {"color": "brown", "name": "camel"}

tests/convert/test_bipartite_graph.py

@@ -81,3 +81,18 @@ def test_from_bipartite_graph(
     # not bipartite
     with pytest.raises(XGIError):
         H = xgi.from_bipartite_graph(bipartite_graph4, dual=True)
+
+
+def test_from_bipartite_graph_to_dihypergraph(
+    bipartite_dihypergraph1
+):
+    H = xgi.from_bipartite_graph(bipartite_dihypergraph1)
+
+    assert set(H.nodes) == {1, 2, 3, 4}
+    assert set(H.edges) == {"a", "b", "c"}
+    assert H.edges.head("a") == {1}
+    assert H.edges.tail("a") == {4}
+    assert H.edges.head("b") == {2}
+    assert H.edges.tail("b") == {1}
+    assert H.edges.head("c") == {3}
+    assert H.edges.tail("c") == {2}

xgi/convert/bipartite_graph.py

@@ -1,10 +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
+from ..generators import empty_hypergraph, empty_dihypergraph
 
 __all__ = ["from_bipartite_graph", "to_bipartite_graph"]
 
@@ -73,14 +74,24 @@ def from_bipartite_graph(G, create_using=None, dual=False):
         else:
             raise XGIError("Invalid type specifier")
 
-    if not bipartite.is_bipartite_node_set(G, nodes):
-        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 = empty_hypergraph(create_using)
     H.add_nodes_from(nodes)
     for edge in edges:
-        nodes_in_edge = list(G.neighbors(edge))
-        H.add_edge(nodes_in_edge, idx=edge)
+        for u, v, d in G.edges(edge, data="direction"):
+            if isinstance(H, xgi.DiHypergraph):
+                if d == "tail":
+                    H.add_node_to_edge(u, v, direction="in")
+                else:
+                    H.add_node_to_edge(u, v, direction="out")
+            else:
+                H.add_node_to_edge(u, v)
     return H.dual() if dual else H