Merge pull request #3899 from rapidsai/branch-23.10

Forward-merge branch-23.10 to branch-23.12

python/cugraph/cugraph/community/louvain.py

@@ -11,7 +11,10 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+from typing import Union, Tuple
+from cugraph.structure import Graph
 from cugraph.utilities import (
+    is_nx_graph_type,
     ensure_cugraph_obj_for_nx,
     df_score_to_dictionary,
 )
@@ -21,9 +24,26 @@
 from pylibcugraph import louvain as pylibcugraph_louvain
 from pylibcugraph import ResourceHandle
 
+from cugraph.utilities.utils import import_optional
+
+# FIXME: the networkx.Graph type used in type annotations is specified
+# using a string literal to avoid depending on and importing networkx.
+# Instead, networkx is imported optionally, which may cause a problem
+# for a type checker if run in an environment where networkx is not installed.
+networkx = import_optional("networkx")
+
+VERTEX_COL_NAME = "vertex"
+CLUSTER_ID_COL_NAME = "partition"
+
 
 # FIXME: max_level should default to 100 once max_iter is removed
-def louvain(G, max_level=None, max_iter=None, resolution=1.0, threshold=1e-7):
+def louvain(
+    G: Union[Graph, "networkx.Graph"],
+    max_level: Union[int, None] = None,
+    max_iter: Union[int, None] = None,
+    resolution: float = 1.0,
+    threshold: float = 1e-7,
+) -> Tuple[Union[cudf.DataFrame, dict], float]:
     """
     Compute the modularity optimizing partition of the input graph using the
     Louvain method
@@ -48,6 +68,9 @@ def louvain(G, max_level=None, max_iter=None, resolution=1.0, threshold=1e-7):
         than the specified number of levels. No error occurs when the
         algorithm terminates early in this manner.
 
+        If max_level > 500, it will be set to 500 and a warning is emitted
+        in order to prevent excessive runtime.
+
     max_iter : integer, optional (default=None)
         This parameter is deprecated in favor of max_level.  Previously
         it was used to control the maximum number of levels of the Louvain
@@ -68,18 +91,21 @@ def louvain(G, max_level=None, max_iter=None, resolution=1.0, threshold=1e-7):
 
     Returns
     -------
-    parts : cudf.DataFrame
-        GPU data frame of size V containing two columns the vertex id and the
-        partition id it is assigned to.
+    result: cudf.DataFrame or dict
+        If input graph G is of type cugraph.Graph, a GPU dataframe
+        with two columns.
+
+            result[VERTEX_COL_NAME] : cudf.Series
+                Contains the vertex identifiers
+            result[CLUSTER_ID_COL_NAME] : cudf.Series
+                Contains the partition assigned to the vertices
 
-        df['vertex'] : cudf.Series
-            Contains the vertex identifiers
-        df['partition'] : cudf.Series
-            Contains the partition assigned to the vertices
+        If input graph G is of type networkx.Graph, a dict
+        Dictionary of vertices and their partition ids.
 
     modularity_score : float
-        a floating point number containing the global modularity score of the
-        partitioning.
+        A floating point number containing the global modularity score
+        of the partitioning.
 
     Examples
     --------
@@ -89,6 +115,17 @@ def louvain(G, max_level=None, max_iter=None, resolution=1.0, threshold=1e-7):
 
     """
 
+    # FIXME: Onece the graph construction calls support isolated vertices through
+    #  the C API (the C++ interface already supports this) then there will be
+    # no need to compute isolated vertices here.
+
+    isolated_vertices = list()
+    if is_nx_graph_type(type(G)):
+        isolated_vertices = [v for v in range(G.number_of_nodes()) if G.degree[v] == 0]
+    else:
+        # FIXME: Gather isolated vertices of G
+        pass
+
     G, isNx = ensure_cugraph_obj_for_nx(G)
 
     if G.is_directed():
@@ -112,7 +149,12 @@ def louvain(G, max_level=None, max_iter=None, resolution=1.0, threshold=1e-7):
     if max_level is None:
         max_level = 100
 
-    vertex, partition, mod_score = pylibcugraph_louvain(
+    if max_level > 500:
+        w_msg = "max_level is set too high, clamping it down to 500."
+        warnings.warn(w_msg)
+        max_level = 500
+
+    vertex, partition, modularity_score = pylibcugraph_louvain(
         resource_handle=ResourceHandle(),
         graph=G._plc_graph,
         max_level=max_level,
@@ -121,14 +163,27 @@ def louvain(G, max_level=None, max_iter=None, resolution=1.0, threshold=1e-7):
         do_expensive_check=False,
     )
 
-    df = cudf.DataFrame()
-    df["vertex"] = vertex
-    df["partition"] = partition
+    result = cudf.DataFrame()
+    result[VERTEX_COL_NAME] = vertex
+    result[CLUSTER_ID_COL_NAME] = partition
+
+    if len(isolated_vertices) > 0:
+        unique_cids = result[CLUSTER_ID_COL_NAME].unique()
+        max_cluster_id = -1 if len(result) == 0 else unique_cids.max()
+
+        isolated_vtx_and_cids = cudf.DataFrame()
+        isolated_vtx_and_cids[VERTEX_COL_NAME] = isolated_vertices
+        isolated_vtx_and_cids[CLUSTER_ID_COL_NAME] = [
+            (max_cluster_id + i + 1) for i in range(len(isolated_vertices))
+        ]
+        result = cudf.concat(
+            [result, isolated_vtx_and_cids], ignore_index=True, sort=False
+        )
 
-    if G.renumbered:
-        df = G.unrenumber(df, "vertex")
+    if G.renumbered and len(G.input_df) > 0:
+        result = G.unrenumber(result, VERTEX_COL_NAME)
 
     if isNx is True:
-        df = df_score_to_dictionary(df, "partition")
+        result = df_score_to_dictionary(result, CLUSTER_ID_COL_NAME)
 
-    return df, mod_score
+    return result, modularity_score

python/cugraph/cugraph/tests/community/test_louvain.py

@@ -142,3 +142,19 @@ def test_louvain_csr_graph(is_weighted):
 
     assert len(parition_diffs) == 0
     assert mod_csr == mod_coo
+
+
+@pytest.mark.sg
+def test_louvain_nx_graph_with_isolated_nodes():
+    # Cluster IDs are expected to unique if all nodes are isolated
+    G = nx.Graph()
+    G.add_nodes_from(range(5))
+    result, _ = cugraph.louvain(G)
+    assert set(result.keys()) == set(G.nodes)
+    assert len(set(result.values())) == G.number_of_nodes()
+
+    # A graph with 5 nodes, where 3 of the nodes are isolated
+    G.add_edge(1, 2)
+    result, _ = cugraph.louvain(G)
+    assert set(result.keys()) == set(G.nodes)
+    assert len(set(result.values())) == G.number_of_nodes() - 1

python/cugraph/cugraph/utilities/utils.py

@@ -364,8 +364,8 @@ def is_matrix_type(m):
     return is_cp_matrix_type(m) or is_sp_matrix_type(m)
 
 
-def is_nx_graph_type(g):
-    return g in __nx_graph_types
+def is_nx_graph_type(graph_type):
+    return graph_type in __nx_graph_types
 
 
 def is_cugraph_graph_type(g):