Fix KDTree node mapping order in connect_nodes_across_graphs(#82)

src/weather_model_graphs/create/base.py

@@ -260,7 +260,12 @@ def connect_nodes_across_graphs(
     target_nodes_list = list(G_target.nodes)
 
     # build kd tree for source nodes (e.g. the mesh nodes when constructing m2g)
-    xy_source = np.array([G_source.nodes[node]["pos"] for node in G_source.nodes])
+    source_nodes_list = list(G_source.nodes)
+
+    xy_source = np.array(
+        [G_source.nodes[node]["pos"] for node in source_nodes_list]
+    )
+
     kdt_s = scipy.spatial.KDTree(xy_source)
 
     # Determine method and perform checks once
@@ -402,7 +407,7 @@ def _find_neighbour_node_idxs_in_source_mesh(xy_target):
     G_connect.add_nodes_from(sorted(G_target.nodes(data=True)))
 
     # sort nodes by index
-    source_nodes_list = sorted(G_source.nodes)
+
 
     # add edges
     for target_node in target_nodes_list:

tests/test_connect_nodes_across_graphs.py

@@ -0,0 +1,35 @@
+import numpy as np
+import networkx as nx
+
+from weather_model_graphs.create.base import connect_nodes_across_graphs
+
+
+def test_kdtree_node_mapping_order():
+    G_source = nx.Graph()
+
+    # intentionally unsorted insertion order
+    G_source.add_node("z", pos=np.array([0.0, 0.0]))
+    G_source.add_node("a", pos=np.array([10.0, 0.0]))
+    G_source.add_node("m", pos=np.array([20.0, 0.0]))
+
+    G_target = nx.Graph()
+
+    G_target.add_node("t0", pos=np.array([0.2, 0.0]))
+    G_target.add_node("t1", pos=np.array([9.9, 0.0]))
+    G_target.add_node("t2", pos=np.array([19.7, 0.0]))
+
+    G = connect_nodes_across_graphs(
+        G_source,
+        G_target,
+        method="nearest_neighbour"
+    )
+
+    edges = sorted(G.edges())
+
+    expected = [
+        ("z", "t0"),
+        ("a", "t1"),
+        ("m", "t2")
+    ]
+
+    assert edges == expected