VertexQ

VertexQ[g,v]

yields True if v is a vertex in the graph g and False otherwise.

Examples

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Basic Examples  (2)

Test whether an item is a vertex of a graph:

Test items of various kinds:

Scope  (5)

VertexQ works with undirected graphs:

Directed graphs:

Multigraphs:

Mixed graphs:

VertexQ works with large graphs:

Compare performance with a test based on VertexList:

Applications  (3)

Check input to a function:

Take the correct action depending on whether an item is a vertex or an edge:

Act on a vertex:

Act on an edge:

Use Graph and VertexQ for fast set membership tests:

Compare with MemberQ:

Properties & Relations  (3)

VertexQ[g,v] is equivalent to MemberQ[VertexList[g],v]:

The performance of VertexQ is typically higher:

Use VertexIndex to find the position of a vertex in VertexList[g]:

VertexIndex is typically faster than Position:

Use EdgeQ to test whether an edge is part of a graph:

Possible Issues  (1)

Some vertices do not seem to be recognized:

Membership is tested using SameQ rather than Equal:

By using identical expressions it can still be tested:

Introduced in 2010
 (8.0)