EdgeRules

Status: Stable

documented, exercised by the test suite and/or worked examples, with no known limitations recorded.

Description

EdgeRules[g]

gives the edges of g as a list of rules u -> v (undirected edges too), in EdgeList order.

Examples (4)

Every input below was run against the current Mathilda build and its output recorded.

Basic examples (3)

In[1]:= EdgeRules[CycleGraph[3]]
Out[1]= {1 -> 2, 2 -> 3, 3 -> 1}

In[2]:= EdgeRules[Graph[{1->2, 2->3}]]
Out[2]= {1 -> 2, 2 -> 3}

In[3]:= EdgeRules[5]
Out[3]= EdgeRules[5]

Applications (1)

Edges as u -> v rules

In[4]:= EdgeRules[Graph[{1 -> 2, 2 -> 3, 3 -> 1, 3 -> 4}]]
Out[4]= {1 -> 2, 2 -> 3, 3 -> 1, 3 -> 4}

Implementation notes

Algorithm. builtin_edge_rules maps each edge of the graph to a Rule u -> v, in EdgeList order. It reads the edge list directly and, for each edge, copies its two endpoints and wraps them in Rule — regardless of whether the edge was a DirectedEdge or an UndirectedEdge. Direction is therefore not encoded in the output: every edge becomes a plain -> rule, which is the form the Graph constructor accepts as input sugar.

Data structures. None beyond the result List of Rule nodes; no adjacency or vertex index is built, and the edge order is the graph's stored order.

Complexity / limits. O(E). Exactly one argument; a non-graph argument returns unevaluated. The result is a plain list of rules, not a Graph.

• Protected. A non-graph argument is left unevaluated.
• Undirected and directed edges both become rules, in EdgeList order.

Attributes: Protected.

References

See also: EdgeList

• Source: src/graph/gops_edit.c
• Specification: docs/spec/builtins/graphs.md
• Tests: tests/test_graph_ops.c

Notes & additional examples

Notes

EdgeRules[g] gives the edges of g as a list of rules u -> v, in EdgeList order. Both directed and undirected edges become plain -> rules — the direction is not preserved in the output, since the point of this form is to feed the edges back into Graph or ReplaceAll.

The result is an ordinary list of Rules, not a graph; use EdgeList if you need the edges with their DirectedEdge / UndirectedEdge heads intact.