From 2d25c77d485a254a05af2bab9e8ad301b2a9eded Mon Sep 17 00:00:00 2001
From: Philipp Rudiger <prudiger@anaconda.com>
Date: Mon, 30 Mar 2020 15:48:42 +0200
Subject: [PATCH] Fix regression in Sankey computation (#4337)

---
 holoviews/element/sankey.py                 |  2 +-
 holoviews/tests/element/testgraphelement.py | 41 +++++++++++++++++++++
 2 files changed, 42 insertions(+), 1 deletion(-)

diff --git a/holoviews/element/sankey.py b/holoviews/element/sankey.py
index 2c1f6f8d95..653d622e15 100644
--- a/holoviews/element/sankey.py
+++ b/holoviews/element/sankey.py
@@ -214,7 +214,7 @@ def computeNodeBreadths(self, graph):
         if py is None:
             max_depth = max(depths.values()) - 1 if depths else 1
             height = self.p.bounds[3] - self.p.bounds[1]
-            py = min((height * 0.1) / max_depth, 20)
+            py = min((height * 0.1) / max_depth, 20) if max_depth else 20
 
         def initializeNodeBreadth():
             kys = []
diff --git a/holoviews/tests/element/testgraphelement.py b/holoviews/tests/element/testgraphelement.py
index a0b48ed896..90309cb40b 100644
--- a/holoviews/tests/element/testgraphelement.py
+++ b/holoviews/tests/element/testgraphelement.py
@@ -11,6 +11,7 @@
 from holoviews.element.graphs import (
     Graph, Nodes, TriMesh, Chord, circular_layout, connect_edges,
     connect_edges_pd)
+from holoviews.element.sankey import Sankey
 from holoviews.element.comparison import ComparisonTestCase
 
 pd_skip = skipIf(util.pd is None, 'Pandas not available')
@@ -294,3 +295,43 @@ def test_trimesh_edgepaths(self):
     def test_trimesh_select(self):
         trimesh = TriMesh((self.simplices, self.nodes)).select(x=(0.1, None))
         self.assertEqual(trimesh.array(), np.array(self.simplices[1:]))
+
+
+class TestSankey(ComparisonTestCase):
+
+    def test_single_edge_sankey(self):
+        sankey = Sankey([('A', 'B', 1)])
+        links = list(sankey._sankey['links'])
+        self.assertEqual(len(links), 1)
+        del links[0]['source']['sourceLinks']
+        del links[0]['target']['targetLinks']
+        link = {
+            'index': 0,
+            'source': {
+                'index': 'A',
+                'values': (),
+                'targetLinks': [],
+                'value': 1,
+                'depth': 0,
+                'height': 1,
+                'x0': 0,
+                'x1': 15,
+                'y0': 0.0,
+                'y1': 500.0},
+            'target': {
+                'index': 'B',
+                'values': (),
+                'sourceLinks': [],
+                'value': 1,
+                'depth': 1,
+                'height': 0,
+                'x0': 985.0,
+                'x1': 1000.0,
+                'y0': 0.0,
+                'y1': 500.0},
+            'value': 1,
+            'width': 500.0,
+            'y0': 0.0,
+            'y1': 0.0
+        }
+        self.assertEqual(links[0], link)