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EdgeIndex[g,e]

gives the integer index for the edge e in the graph g.

EdgeIndex[{vw,…},…]

uses rules vw to specify the graph g.

Details
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Examples  
Basic Examples  
Scope  
Properties & Relations  
Possible Issues  
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EdgeIndex

EdgeIndex[g,e]

gives the integer index for the edge e in the graph g.

EdgeIndex[{vw,…},…]

uses rules vw to specify the graph g.

Details

Examples

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Basic Examples  (1)

Find the integer index of an edge:

Wolfram Language code: g = [image];
Wolfram Language code: EdgeIndex[g, 411]

The index corresponds to the position in the edge list:

Wolfram Language code: EdgeList[g][[%]]

Scope  (4)

EdgeIndex works with undirected graphs:

Wolfram Language code: EdgeIndex[[image], ab]

Directed graphs:

Wolfram Language code: EdgeIndex[[image], ab]

Use rules to specify the graph:

Wolfram Language code: EdgeIndex[{a -> b, b -> c, c -> a}, ab]

EdgeIndex works with large graphs:

Wolfram Language code: g = GridGraph[{10, 10, 10, 10}];
Wolfram Language code: Timing[EdgeIndex[g, 12]]

Properties & Relations  (5)

The EdgeIndex of an edge corresponds to its position in EdgeList:

Wolfram Language code: g = CompleteGraph[4, DirectedEdges -> True, EdgeStyle -> Arrowheads[Small]]
Wolfram Language code: Table[EdgeList[g][[EdgeIndex[g, e]]] === e, {e, EdgeList[g]}]

Sort the vertices in undirected edges for comparison:

Wolfram Language code: g = CompleteGraph[4]
Wolfram Language code: Table[Sort[EdgeList[g][[EdgeIndex[g, e]]]] === Sort[e], {e, EdgeList[g]}]

EdgeIndex is typically faster than Position:

Wolfram Language code: g = GridGraph[{10, 10, 10, 10}];
Wolfram Language code: {Timing[EdgeIndex[g, 12]], Timing[Position[EdgeList[g], 12 | 21]]}

EdgeQ can be used to tell whether EdgeIndex will succeed:

Wolfram Language code: g = [image];

Try an edge item:

Wolfram Language code: {EdgeQ[g, 32], EdgeIndex[g, 32]}

Try a non-edge item:

Wolfram Language code: {EdgeQ[g, 24], EdgeIndex[g, 24]}

Use VertexIndex to find the integer index of a vertex:

Wolfram Language code: VertexIndex[Graph[{23, 31}], 2]

VertexIndex and EdgeIndex give the row and column ordering used in IncidenceMatrix:

Wolfram Language code: g = Graph[{ad, ab, bc, cd}];
Wolfram Language code: (m = IncidenceMatrix[g])//MatrixForm

Test whether is incident to :

Wolfram Language code: m[[VertexIndex[g, a], EdgeIndex[g, ad]]]

Possible Issues  (1)

Some edges do not seem to have integer indices:

Wolfram Language code: v = Block[{ϵ = 10 ^ -15}, Range[1.1, 1.4, 0.1] + ϵ]
Wolfram Language code: g = Graph[v, Table[v[[i]]v[[i + 1]], {i, 1, 3}], VertexShapeFunction -> "Name"]
Wolfram Language code: EdgeIndex[g, 1.11.2]

Membership is tested using SameQ rather than Equal:

Wolfram Language code: {v[[1]]v[[2]] === 1.11.2, v[[1]]v[[2]] == 1.11.2}

By using identical expressions, the integer index is found:

Wolfram Language code: EdgeIndex[g, v[[1]]v[[2]]]
Wolfram Research (2010), EdgeIndex, Wolfram Language function, https://reference.wolfram.com/language/ref/EdgeIndex.html (updated 2015).

Text

Wolfram Research (2010), EdgeIndex, Wolfram Language function, https://reference.wolfram.com/language/ref/EdgeIndex.html (updated 2015).

CMS

Wolfram Language. 2010. "EdgeIndex." Wolfram Language & System Documentation Center. Wolfram Research. Last Modified 2015. https://reference.wolfram.com/language/ref/EdgeIndex.html.

APA

Wolfram Language. (2010). EdgeIndex. Wolfram Language & System Documentation Center. Retrieved from https://reference.wolfram.com/language/ref/EdgeIndex.html

BibTeX

@misc{reference.wolfram_2026_edgeindex, author="Wolfram Research", title="{EdgeIndex}", year="2015", howpublished="\url{https://reference.wolfram.com/language/ref/EdgeIndex.html}", note=[Accessed: 12-June-2026]}

BibLaTeX

@online{reference.wolfram_2026_edgeindex, organization={Wolfram Research}, title={EdgeIndex}, year={2015}, url={https://reference.wolfram.com/language/ref/EdgeIndex.html}, note=[Accessed: 12-June-2026]}