Use dataframe index for TriMesh node indices

holoviews/element/graphs.py

@@ -6,7 +6,7 @@
 
 from ..core import Dimension, Dataset, Element2D
 from ..core.accessors import Redim
-from ..core.util import max_range, search_indices
+from ..core.util import is_dataframe, max_range, search_indices
 from ..core.operation import Operation
 from .chart import Points
 from .path import Path
@@ -545,15 +545,20 @@ def __init__(self, data, kdims=None, vdims=None, **params):
             # Add index to make it a valid Nodes object
             nodes = self.node_type(Dataset(nodes).add_dimension('index', 2, np.arange(len(nodes))))
         elif not isinstance(nodes, Dataset) or nodes.ndims in [2, 3]:
-            # Try assuming data contains just coordinates (2 columns)
-            try:
-                points = self.point_type(nodes)
-                ds = Dataset(points).add_dimension('index', 2, np.arange(len(points)))
-                nodes = self.node_type(ds)
-            except:
-                raise ValueError("Nodes argument could not be interpreted, expected "
-                                 "data with two or three columns representing the "
-                                 "x/y positions and optionally the node indices.")
+            if is_dataframe(nodes):
+                coords = list(nodes.columns)[:2]
+                index = nodes.index.name or 'index'
+                nodes = self.node_type(nodes, coords+[index])
+            else:
+                try:
+                    points = self.point_type(nodes)
+                    ds = Dataset(points).add_dimension('index', 2, np.arange(len(points)))
+                    nodes = self.node_type(ds)
+                except Exception:
+                    raise ValueError(
+                        "Nodes argument could not be interpreted, expected "
+                        "data with two or three columns representing the "
+                        "x/y positions and optionally the node indices.")
         if edgepaths is not None and not isinstance(edgepaths, self.edge_type):
             edgepaths = self.edge_type(edgepaths)
 

holoviews/tests/operation/testdatashader.py

@@ -922,6 +922,46 @@ def test_rasterize_trimesh(self):
         image = Image(array, bounds=(0, 0, 1, 1))
         self.assertEqual(img, image)
 
+    def test_rasterize_pandas_trimesh_implicit_nodes(self):
+        simplex_df = pd.DataFrame(self.simplexes, columns=['v0', 'v1', 'v2'])
+        vertex_df = pd.DataFrame(self.vertices_vdim, columns=['x', 'y', 'z'])
+
+        trimesh = TriMesh((simplex_df, vertex_df))
+        img = rasterize(trimesh, width=3, height=3, dynamic=False)
+
+        array = np.array([
+            [    2.,     3., np.NaN],
+            [   1.5,    2.5, np.NaN],
+            [np.NaN, np.NaN, np.NaN]
+        ])
+        image = Image(array, bounds=(0, 0, 1, 1))
+        self.assertEqual(img, image)
+
+    def test_rasterize_dask_trimesh_implicit_nodes(self):
+        simplex_df = pd.DataFrame(self.simplexes, columns=['v0', 'v1', 'v2'])
+        vertex_df = pd.DataFrame(self.vertices_vdim, columns=['x', 'y', 'z'])
+
+        simplex_ddf = dd.from_pandas(simplex_df, npartitions=2)
+        vertex_ddf = dd.from_pandas(vertex_df, npartitions=2)
+
+        trimesh = TriMesh((simplex_ddf, vertex_ddf))
+
+        ri = rasterize.instance()
+        img = ri(trimesh, width=3, height=3, dynamic=False, precompute=True)
+
+        cache = ri._precomputed
+        self.assertEqual(len(cache), 1)
+        self.assertIn(trimesh._plot_id, cache)
+        self.assertIsInstance(cache[trimesh._plot_id]['mesh'], dd.DataFrame)
+
+        array = np.array([
+            [    2.,     3., np.NaN],
+            [   1.5,    2.5, np.NaN],
+            [np.NaN, np.NaN, np.NaN]
+        ])
+        image = Image(array, bounds=(0, 0, 1, 1))
+        self.assertEqual(img, image)
+
     def test_rasterize_dask_trimesh(self):
         simplex_df = pd.DataFrame(self.simplexes_vdim, columns=['v0', 'v1', 'v2', 'z'])
         vertex_df = pd.DataFrame(self.vertices, columns=['x', 'y'])