bug fix for draw_dihypergraph

tests/drawing/test_draw.py

@@ -230,7 +230,9 @@ def test_draw_dihypergraph(diedgelist2, edgelist8):
     # number of elements
     assert len(ax1.lines) == 7  # number of source nodes
     assert len(ax1.patches) == 4  # number of target nodes
-    assert len(ax1.collections) == DH.num_edges + 1  # hyperedges markers + nodes
+    assert len(ax1.collections) == DH.num_edges + 1 - len(
+        DH.edges.filterby("size", 1)
+    )  # hyperedges markers + nodes
 
     # zorder
     for line, z in zip(ax1.lines, [1, 1, 1, 1, 0, 0, 0]):  # lines for source nodes
@@ -253,3 +255,20 @@ def test_draw_dihypergraph(diedgelist2, edgelist8):
         H = xgi.Hypergraph(edgelist8)
         ax3 = xgi.draw_dihypergraph(H)
         plt.close()
+
+
+def test_draw_dihypergraph_with_str_labels_and_isolated_nodes():
+    DH1 = xgi.DiHypergraph()
+    DH1.add_edges_from(
+        [
+            [{"one"}, {"two", "three"}],
+            [{"two", "three"}, {"four", "five"}],
+            [{"six"}, {}],
+        ]
+    )
+    ax4 = xgi.draw_dihypergraph(DH1)
+    assert len(ax4.lines) == 3
+    assert len(ax4.patches) == 4
+    assert len(ax4.collections) == DH1.num_edges + 1 - len(
+        DH1.edges.filterby("size", 1)
+    )

xgi/drawing/draw.py

@@ -1633,61 +1633,66 @@ def draw_dihypergraph(
 
     G_aug = _augmented_projection(H_conv)
     for dyad in H_conv.edges.filterby("size", 2).members():
-        index = max(G_aug.nodes) + 1
+        try:
+            index = max(n for n in G_aug.nodes if isinstance(n, int)) + 1
+        except ValueError:
+            # The list of node-labels has no integers, so I start from 0
+            index = 0
         G_aug.add_edges_from([[list(dyad)[0], index], [list(dyad)[1], index]])
 
     phantom_nodes = [n for n in list(G_aug.nodes) if n not in list(H_conv.nodes)]
     pos = spring_layout(G_aug)
 
     for id, he in DH.edges.members(dtype=dict).items():
         d = len(he) - 1
-        # identify the center of the edge in the augemented projection
-        center = [n for n in phantom_nodes if set(G_aug.neighbors(n)) == he][0]
-        x_center, y_center = pos[center]
-        for node in DH.edges.dimembers(id)[0]:
-            x_coords = [pos[node][0], x_center]
-            y_coords = [pos[node][1], y_center]
-            line = plt.Line2D(
-                x_coords,
-                y_coords,
-                color=lines_fc[id],
-                lw=lines_lw[id],
-                zorder=max_order - d,
-            )
-            ax.add_line(line)
-        for node in DH.edges.dimembers(id)[1]:
-            dx, dy = pos[node][0] - x_center, pos[node][1] - y_center
-            # the following to avoid the point of the arrow overlapping the node
-            distance = np.hypot(dx, dy)
-            direction_vector = np.array([dx, dy]) / distance
-            shortened_distance = (
-                distance - node_size[node] * 0.003
-            )  # Calculate the shortened length
-            dx = direction_vector[0] * shortened_distance
-            dy = direction_vector[1] * shortened_distance
-            arrow = FancyArrow(
-                x_center,
-                y_center,
-                dx,
-                dy,
-                color=lines_fc[id],
-                width=lines_lw[id] * 0.001,
-                length_includes_head=True,
-                head_width=line_head_width,
-                zorder=max_order - d,
-            )
-            ax.add_patch(arrow)
-        if edge_marker_toggle:
-            ax.scatter(
-                x=x_center,
-                y=y_center,
-                marker=edge_marker,
-                s=edge_marker_size**2,
-                c=edge_marker_fc[id],
-                edgecolors=edge_marker_ec[id],
-                linewidths=edge_marker_lw,
-                zorder=max_order,
-            )
+        if d > 0:
+            # identify the center of the edge in the augemented projection
+            center = [n for n in phantom_nodes if set(G_aug.neighbors(n)) == he][0]
+            x_center, y_center = pos[center]
+            for node in DH.edges.dimembers(id)[0]:
+                x_coords = [pos[node][0], x_center]
+                y_coords = [pos[node][1], y_center]
+                line = plt.Line2D(
+                    x_coords,
+                    y_coords,
+                    color=lines_fc[id],
+                    lw=lines_lw[id],
+                    zorder=max_order - d,
+                )
+                ax.add_line(line)
+            for node in DH.edges.dimembers(id)[1]:
+                dx, dy = pos[node][0] - x_center, pos[node][1] - y_center
+                # the following to avoid the point of the arrow overlapping the node
+                distance = np.hypot(dx, dy)
+                direction_vector = np.array([dx, dy]) / distance
+                shortened_distance = (
+                    distance - node_size[node] * 0.003
+                )  # Calculate the shortened length
+                dx = direction_vector[0] * shortened_distance
+                dy = direction_vector[1] * shortened_distance
+                arrow = FancyArrow(
+                    x_center,
+                    y_center,
+                    dx,
+                    dy,
+                    color=lines_fc[id],
+                    width=lines_lw[id] * 0.001,
+                    length_includes_head=True,
+                    head_width=line_head_width,
+                    zorder=max_order - d,
+                )
+                ax.add_patch(arrow)
+            if edge_marker_toggle:
+                ax.scatter(
+                    x=x_center,
+                    y=y_center,
+                    marker=edge_marker,
+                    s=edge_marker_size**2,
+                    c=edge_marker_fc[id],
+                    edgecolors=edge_marker_ec[id],
+                    linewidths=edge_marker_lw,
+                    zorder=max_order,
+                )
 
     if hyperedge_labels:
         # Get all valid keywords by inspecting the signatures of draw_node_labels