I have a list of directed edges for a graph and I want to replace all edges that match a certain pattern. The edges should be replaced by a number. It ends up in a edge weighting list for a graph. All edges that go to "window" should have the same weight. Therefore the replacement. I tried this:

ReplaceList[{"a" \[DirectedEdge] "window", 
  "window" \[DirectedEdge] "door"}, 
 y_ \[DirectedEdge] x_ /; x == "window" -> 2]

The pattern matching does not work in this case. The goal is to replace only edges were "window" is the receiving vertex. Is there a way to do it in similar fashion to above trial? Can the pattern matching made to work in ReplaceList?


1 Answer 1


You can use Replace with level specification All:

Replace[{"a" \[DirectedEdge] "window", "window" \[DirectedEdge] "door"}, 
 y_ \[DirectedEdge] x_ /; x == "window" -> 2, All]

or, shorter,

Replace[{"a" \[DirectedEdge] "window", "window" \[DirectedEdge] "door"},
   _ \[DirectedEdge] "window" ->  2, All]


Replace[{"a" \[DirectedEdge] "window", "window" \[DirectedEdge] "door"}, 
 DirectedEdge[_, "window"] -> 2, All]

to get

 {2, "window" \[DirectedEdge] "door"}

Note: As commented by @Szabolcs, DirectedEdge may have three arguments in version 12.1. So if the input list contains tagged edges we can use the replacement rule

DirectedEdge[_, "window", ___] -> 2
  • 1
    $\begingroup$ DirectedEdge may have a 3rd argument in 12.1 (EdgeTaggedGraph) $\endgroup$
    – Szabolcs
    Apr 15, 2020 at 7:51

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