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Given:

dag1 = {"scst" \[DirectedEdge] "stel", "scst" \[DirectedEdge] "sfin", 
   "scst" \[DirectedEdge] "sbus", "scst" \[DirectedEdge] "swhl", 
   "scst" \[DirectedEdge] "ma6", "sfin" \[DirectedEdge] "stel", 
   "sfin" \[DirectedEdge] "sbus", "sfin" \[DirectedEdge] "swhl", 
   "sbus" \[DirectedEdge] "stel", "sbus" \[DirectedEdge] "ma6", 
   "swhl" \[DirectedEdge] "sbus", "swhl" \[DirectedEdge] "ma6"};

The following code intends to extract all the edges directed towards the vertex "sfin". However, it gives an empty set!

EdgeList[dag1, _ -> "sfin"]

Given a directed graph dag1, I like to extract the set of vertices having directed edges towards vertex "sfin", such as

{"sfin", "scst"}       for vertex "sfin"
{"bus", "stel", "ma6"} for vertex "sbus", etc. 

Note that the vertex of interest is the first element in the above two example sets.

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1 Answer 1

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Inside EdgeList you must use DirectedEdge instead of Rule

EdgeList[dag1, _ \[DirectedEdge] "sfin"]

enter image description here

EdgeList[dag1, _ \[DirectedEdge] "sfin" | "sfin" \[DirectedEdge] _]

enter image description here

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  • $\begingroup$ Why? In the documentation, a directed arrow is used, which I replicated it. I got it. The shape of the arrow is slightly different!!! $\endgroup$ Nov 6, 2023 at 18:54
  • $\begingroup$ The second part of my question is to construct the vertex sets as described in the question above. Can you also address to that? $\endgroup$ Nov 6, 2023 at 18:59
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    $\begingroup$ @TugrulTemel VertexInComponent[dag1, "sfin"] or VertexOutComponent[dag1, "sbus", 1] ? $\endgroup$
    – halmir
    Nov 6, 2023 at 19:51
  • $\begingroup$ @halmir: VertexIn/Out components give a different result. I simply like to get the list of vertices having directed In links to a given vertex. Since the graph given dag1 is a layered DAG, the result should be a list of vertices (acting as inputs) to a given vertex. I want to write the DAG as a set of functions, such as "sfin"=f["scst"] or "swhl"=f["scst", "sfin"] etc. $\endgroup$ Nov 6, 2023 at 21:06

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