K-Core

UDTF: cugraph_k_core

Official cuGraph reference: C API

Return the edges of the maximal subgraph whose vertices each have degree at least k within that subgraph.

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_k_core(
  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

Option	Type	Default	Constraints	Description
degree_type	string	"in_out"	one of "in", "out", "in_out"	degree direction
k	integer	2	min 1; max 4294967295	k-core degree threshold, at least 1

Graph construction options

This UDTF 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
src	Int64|Utf8	no	Source vertex of an edge retained in the k-core subgraph.
dst	Int64|Utf8	no	Destination vertex of an edge retained in the k-core subgraph.

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

Examples

This example runs on the citation network demo dataset.

Which papers stand out inside the densely connected citation core?

The k=30 core keeps papers with at least 30 neighbors inside the core when citation links are treated as undirected. Its edge output is symmetrized, so a retained neighbor pair appears in both directions. This threshold counts undirected neighbors, not at least 30 citations received and 30 references made by every paper. The nested call passes the core directly to PageRank and returns its five highest-scoring papers:

SELECT p.year, p.title
FROM cugraph_pagerank(edges => (
  SELECT src, dst
  FROM cugraph_k_core(
    edges => (SELECT src, dst FROM citation_edges), k => 30)
)) r
JOIN papers p ON p.paper_id = r.vertex
ORDER BY r.value DESC
LIMIT 5;

year	title
2004	Distinctive Image Features from Scale-Invariant Keypoints
2014	VERY DEEP CONVOLUTIONAL NETWORKS FOR LARGE-SCALE IMAGE RECOGNITION
2005	Histograms of oriented gradients for human detection
2009	ImageNet: A large-scale hierarchical image database
2016	Deep Residual Learning for Image Recognition

Limits

No algorithm-specific limitations.

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