From 1f51968bca667cf9bd59edbdb8bb940d36bff331 Mon Sep 17 00:00:00 2001
From: Tom Russell <tom.russell@ouce.ox.ac.uk>
Date: Tue, 6 Feb 2024 16:31:31 +0000
Subject: [PATCH] Start writing merge_networks

---
 src/snkit/network.py | 28 ++++++++++++++++++++++++++++
 tests/test_init.py   | 20 ++++++++++++++++++++
 2 files changed, 48 insertions(+)

diff --git a/src/snkit/network.py b/src/snkit/network.py
index 7154f63..817a0a3 100644
--- a/src/snkit/network.py
+++ b/src/snkit/network.py
@@ -1040,3 +1040,31 @@ def add_component_ids(network: Network, id_col: str = "component_id") -> Network
         network.nodes.loc[node_mask, id_col] = count + 1
 
     return network
+
+
+def merge_networks(networks: List[Network]) -> Network:
+    """Merge multiple networks, identifying duplicate nodes at shared locations"""
+
+    n = len(networks)
+    if n == 0:
+        warnings.warn("Merging zero networks to return empty network.")
+        return Network()
+    if n == 1:
+        return networks[0]
+
+    # TODO update components
+    # - find duplicated nodes by location
+    # - for each duplicated node, record (network_idx, component_id)
+    # - set up nx.Graph
+    #   - a vertex for each duplicated node
+    #   - edges connecting duplicate node sets
+    #   - edges connecting (network_idx, component_id) sets
+    #   - find connected components in this graph
+    # - set up Dict[Tuple[network_idx, component_id], global_component_id]
+
+    # TODO do we default to concat_dedup? or default low-intervention?
+    # TODO how to handle expectations of unique node or edge ids? (especially if edges have topology)
+    nodes = concat_dedup([network.nodes for network in networks])
+    edges = concat_dedup([network.edges for network in networks])
+
+    return Network(nodes, edges)
diff --git a/tests/test_init.py b/tests/test_init.py
index 827bba7..e9a158b 100644
--- a/tests/test_init.py
+++ b/tests/test_init.py
@@ -838,6 +838,26 @@ def test_add_component_ids(two_components):
     assert all(labelled.edges.component_id == pd.Series([2, 1, 1]))
 
 
+def test_merge_zero_networks():
+    merged = snkit.network.merge_networks([])
+    assert merged.nodes.empty
+    assert merged.edges.empty
+
+
+def test_merge_one_network(split):
+    merged = snkit.network.merge_networks([split])
+    assert_frame_equal(merged.nodes, split.nodes)
+    assert_frame_equal(merged.edges, split.edges)
+
+
+def test_merge_networks(split):
+    split_abc = snkit.Network(split.nodes[:3], split.edges[:2])
+    split_cd = snkit.Network(split.nodes[2:], split.edges[2:])
+    merged = snkit.network.merge_networks([split_abc, split_cd])
+    assert_frame_equal(merged.nodes, split.nodes)
+    assert_frame_equal(merged.edges, split.edges)
+
+
 def test_matching_gdf_from_geoms(edge_only):
     expected = edge_only.edges.copy()
     gdf = edge_only.edges.copy()