Vertex Labelling and Word wrap

Question

I am having trouble formatting vertex labels, explicitly adding line breaks to Vertex labels for word wrapping and other purposes.  I have explored the pane option suggested here but when I include StringReplace it starts throwing errors although still gives the required result.  I suspect its due to incomplete understanding of what "Names" does.

My example is as follows - note I'm creating an Org chart hence the custom (and somewhat "wordy" EdgeLayout.

I realise I can probably get a more complex Vertex label by using Table and a replacement rule - but I'll also need a simpler form for other purposes so it would be good to fix this one first.

So 2 parts to my question.

How to avoid the errors?
Whats actually passed to a function when "Names" is used?

wrapLabel[lbl_] := StringReplace[lbl, ":" -> "n"];

Graph[{"Melvyn:GRU"-> "Gordon:Minion 1","Melvyn:GRU"->"Philip:Minion 2"},
    {GraphStyle->"SmallNetwork",
    EdgeShapeFunction->  (*Edges consist of 3 pairs of 2d cords to create a typical Org Chart style 3 Line Edge *)({Line[{#1[[1]](*1st pair*),{#1[[1,1]],#1[[1,2]]-(#1[[1,2]]-#1[[2,2]])/2}(*2nd pair*),{#1[[1,1]],#1[[1,2]]-(#1[[1,2]]-#1[[2,2]])/2}(*3rd pair*),{#1[[2,1]],(#1[[1,2]]-(#1[[1,2]]-#1[[2,2]])/2)}(*4th pair*),{#1[[2,1]],(#1[[1,2]]-(#1[[1,2]]-#1[[2,2]])/2)}(*5th pair*),#1[[2]] (*6th pair*)}]}&),
    EdgeStyle-> {DirectedEdge["Melvyn:GRU","Gordon:Minion 1"]->Dashed },
    ImageSize->{1200,Automatic},
    GridLinesStyle->Directive[GrayLevel[0.5,0.4]],
    VertexLabels->{Placed["Name",Center,wrapLabel]},
    VertexShapeFunction->{"RoundedRectangle"},
    VertexStyle->{"Philip:Minion 2"-> Green}}]

Error given

String or list of strings expected at position 1 in StringReplace[!(#2, ":" -> "
")].

kglr · Accepted Answer

ClearAll[wrapLabel];
wrapLabel[lbl_] := StringReplace[lbl, ":" -> "n"];
vlist={"Melvyn:GRU", "Gordon:Minion 1",  "Philip:Minion 2"};

options = {GraphStyle -> "SmallNetwork", 
   EdgeShapeFunction ->
  (*Edges consist of 3 pairs of 2d cords to create a typical Org Chart style 3 Line Edge*)
   ({Line[{#1[[1]](*1st pair*), 
     {#1[[1, 1]], #1[[1, 2]] - (#1[[1, 2]] - #1[[2, 2]])/ 2}(*2nd pair*), 
     {#1[[1, 1]], #1[[1, 2]] - (#1[[1, 2]] - #1[[2, 2]])/ 2}(*3rd pair*),
     {#1[[2, 1]], (#1[[1, 2]] - (#1[[1, 2]] - #1[[2, 2]])/2)}(*4th pair*),
     {#1[[2, 1]], (#1[[1, 2]] - (#1[[1, 2]] - #1[[2, 2]])/2)}(*5th pair*),
      #1[[2]] (*6th pair*)}]} &), 
   EdgeStyle -> {DirectedEdge["Melvyn:GRU", "Gordon:Minion 1"] -> Dashed}, 
   (* ImageSize -> {1200, Automatic},  removed *)
   ImageSize -> {500, 200}, (* added  *)
   VertexSize -> Large, (* added *)
   GridLinesStyle -> Directive[GrayLevel[0.5, 0.4]],
   VertexLabels -> Placed["Name", Center, wrapLabel],
   VertexShapeFunction -> {"RoundedRectangle"}, 
   VertexStyle -> {"Philip:Minion 2" -> Green}};

The function wrapLabel in the third argument of Placed:

gg = Graph[{"Melvyn:GRU" -> "Gordon:Minion 1", "Melvyn:GRU" -> "Philip:Minion 2"}, options]

gives (without an error message in Version 9, and accompanied by error messages in Version 10)

The easiest solution is to change the definition of wrapLabel to wrapLabel[lbl_String]:=... as suggested by Bob Hanlon in the comments.

Here are some additional methods that work with OP's definition as is:

Use an alternative syntax for setting VertexLabels

Graph[{"Melvyn:GRU" -> "Gordon:Minion 1", "Melvyn:GRU" -> "Philip:Minion 2"}, 
      VertexLabels -> {x_ :> Placed[wrapLabel[x], Center]}, options]
(* or VertexLabels -> {x_ :> Placed[x, Center,wrapLabel]} *)

or

Graph[{"Melvyn:GRU" -> "Gordon:Minion 1", "Melvyn:GRU" -> "Philip:Minion 2"}, 
      VertexLabels ->  Placed[# ,Center,wrapLabel]&/@vlist, options]
(* or VertexLabels ->  Placed[wrapLabel@#,Center]&/@vlist *)

Post-process to set the VertexLabels using SetProperty

wrappedLabelsF = Fold[SetProperty[{#, #2},  VertexLabels -> 
                       Placed[wrapLabel[#2], Center]] &, #, VertexList[#]] &;
wrappedLabelsF@gg

Use the first argument of Graph to provide a labeled vertex list using Property

Graph[Property[#,  VertexLabels -> Placed[wrapLabel[#], Center]] & /@ vlist,
      {"Melvyn:GRU" -> "Gordon:Minion 1", "Melvyn:GRU" -> "Philip:Minion 2"}, options]

All give

Vertex Labelling and Word wrap

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