Weakly Connected Components

SQL function: cugraph_weakly_connected_components

Official cuGraph reference: C API

Label maximal connected subgraphs after treating directed edges as undirected.

Quickstart

The call below supplies edges from registered relation target_edges with canonical src and dst columns and may include weight. Substitute your own registered relations.

SELECT * FROM cugraph_weakly_connected_components(edges => (SELECT src, dst FROM target_edges));

Inputs

Every relation is a named parenthesized SELECT subquery. The required edges role uses canonical src and dst columns; every role, its canonical columns, and their accepted Arrow types are listed under Relation arguments. Metadata validation resolves registered tables named in its JSON request.

Endpoint columns accept numeric Int32, Int64 vertex IDs or logical string Utf8, LargeUtf8, Utf8View vertex IDs; string vertex-identity outputs are canonicalized to Utf8 (native mapping Int64) while scores, distances, counts, coordinates, and opaque labels stay numeric. The shared vertex-ID contract is summarized in Vertex ID support; the concrete call-specific schema comes from gpu_validate_call.

Logical string side-input limitations:

• edge ID columns and edge-ID predicate side inputs are not supported for logical string graphs

Arguments and options

Relation arguments

Argument	Required	Columns	Description
edges	yes	src, dst: Int32, Int64, Utf8, LargeUtf8, Utf8View weight (optional): Float32, Float64 edge_id (optional): Int32, Int64	edge relation with canonical src and dst columns, plus optional weight and edge_id columns

Every edge_id column must have the integer type of src and dst; string-keyed graphs accept no edge IDs.

Named value arguments

This function has no algorithm-specific value arguments. Its inputs are the relation arguments above and the graph construction options below.

Graph construction options

This function requires directed=false (undirected/symmetric graph); all other graph construction options follow the shared defaults documented in Graph Construction Options.

Output

Column	Type	Nullable	Description
vertex	Int64|Utf8	no	Vertex assigned to a weakly connected component.
label	Int64	no	Weakly connected component identifier for the vertex: the minimum vertex id in the component, stable across runs.

These are generic descriptor schemas; run gpu_validate_call to get the concrete, table-specific output schema.

Examples

These examples run on the citation network demo dataset.

Measure the largest connected component

WCC requires directed: false. Of the 4.15M papers that have at least one edge, 99.4% form a single giant component:

WITH comp AS (
  SELECT label, COUNT(*) AS members
  FROM cugraph_weakly_connected_components(
    edges => (SELECT src, dst FROM citation_edges), directed => false)
  GROUP BY label)
SELECT COUNT(*) AS components, MAX(members) AS giant, SUM(members) AS vertices
FROM comp;

components	giant	vertices
9,751	4,123,602	4,146,772

Snapshot first, then examine the isolated components

Component labels are assigned per execution, so a query that scans the algorithm twice can join mismatched labels. Materialize one run in the mutable datafusion.public workspace, then summarize the largest components outside the giant one: one row per component, represented by its most-cited member.

-- Local workspace snapshot; this does not write to lake.citation_network.
CREATE OR REPLACE TABLE wcc_snapshot AS
SELECT vertex, label
FROM cugraph_weakly_connected_components(
  edges => (SELECT src, dst FROM citation_edges), directed => false);

WITH sizes AS (
  SELECT label, COUNT(*) AS members FROM wcc_snapshot
  GROUP BY label ORDER BY members DESC LIMIT 3 OFFSET 1),
detail AS (
  SELECT s.members, p.year, p.venue, p.title,
         ROW_NUMBER() OVER (PARTITION BY s.label ORDER BY p.n_citation DESC) AS rn
  FROM sizes s
  JOIN wcc_snapshot c ON c.label = s.label
  JOIN papers p ON p.paper_id = c.vertex)
SELECT members, year, venue, title
FROM detail WHERE rn = 1
ORDER BY members DESC;

members	year	venue	title
39	2008	IEICE Transactions on Electronics	Motion of Break Arcs Driven by External Magnetic Field…
25	2013	IEICE Electronics Express	Cavity-resonator-integrated guided-mode resonance filter…
21	2015	Symmetry	Inflationary Cosmology in Modified Gravity Theories

The three largest isolated components are a 39-paper cluster on electrical-contact arc discharge, a 25-paper photonics/electromagnetics cluster, and a 21-paper modified-gravity cosmology cluster, each citing only itself. Communities that publish outside the corpus's main subject areas appear as disconnected components in the graph.

Limits

• cuGraph requires directed=false so the graph is constructed as an undirected/symmetric view

To dry-run validate relation metadata, column types, and options without execution, see gpu_validate_call.