Bugfix for issue 5123 (#5153)

* fixed bug in multipartite_layout so subset labels can be non-numeric

* Added non-numeric partition label test to test_multipartite_layout.

* moved multipartite non-numeric partition label test outside of main test class

Co-authored-by: Ross Barnowski <rossbar@berkeley.edu>

2 files changed, 13 insertions, 1 deletions

diff --git a/networkx/drawing/layout.py b/networkx/drawing/layout.py
index ca0f0437..c16446e2 100644
--- a/networkx/drawing/layout.py
+++ b/networkx/drawing/layout.py
@@ -1092,7 +1092,7 @@ def multipartite_layout(G, subset_key="subset", align="vertical", scale=1, cente
     nodes = []
 
     width = len(layers)
-    for i, layer in layers.items():
+    for i, layer in enumerate(layers.values()):
         height = len(layer)
         xs = np.repeat(i, height)
         ys = np.arange(0, height, dtype=float)
diff --git a/networkx/drawing/tests/test_layout.py b/networkx/drawing/tests/test_layout.py
index 183c9fbc..ab973088 100644
--- a/networkx/drawing/tests/test_layout.py
+++ b/networkx/drawing/tests/test_layout.py
@@ -412,3 +412,15 @@ class TestLayout:
         }
         for k, v in expectation.items():
             assert (s_vpos[k] == v).all()
+
+
+def test_multipartite_layout_nonnumeric_partition_labels():
+    """See gh-5123."""
+    G = nx.Graph()
+    G.add_node(0, subset="s0")
+    G.add_node(1, subset="s0")
+    G.add_node(2, subset="s1")
+    G.add_node(3, subset="s1")
+    G.add_edges_from([(0, 2), (0, 3), (1, 2)])
+    pos = nx.multipartite_layout(G)
+    assert len(pos) == len(G)