How to extract argument of MeshRegion-Object?

Question

Consider examplary a MeshRegion-Object

test = MeshRegion[{{0, 0}, {1, 0}, {2,1/2}, {2, -1/2}}, {Line[{1, 2}], Line[{2, 3}],Line[{3, 4}],Line[{4, 2}]}];

Looking inside test I get

??test
(*Global`test
 MeshRegion[...]*)

To extract the arguments of MeshRegion I usually try

test /. MeshRegion->List

which doesn't work in this example?

What might be the reason? Is there a workaround? Thanks

maybe MeshCoordinates[test]and MeshCells[test, 1] or MeshCells[test, All]? — kglr, Jan 15 '19 at 07:48
@kglr Thanks, that would return the "input arguments". My goal is to pick everything inside the MeshRegion[...]-expression which ??test returns. — Ulrich Neumann, Jan 15 '19 at 07:53
Well, you shouldn't. MeshRegion is atomic. The "input form" may not even correspond accurately to the internal representation (though I believe in this case it does). Use the documented API if you need guarantees and protection from breakage in special cases or future/past versions. All that said, check out my community wiki answer (or Carl's Nucleus) in the QA I linked above. — Szabolcs, Jan 15 '19 at 08:50
@ user21 I think Mesh is an option for Plot3D&Co and MeshRegion is some kind of mesh-object. Sorry, no more insight. — Ulrich Neumann, Feb 18 '19 at 08:57

score 1 · Answer 1 · answered Jan 15 '19 at 09:01

Maybe

ReleaseHold[ToExpression[ToBoxes[InputForm[test]][[1, 1]], StandardForm, Hold] /. 
  MeshRegion -> List]

{{{0., 0.}, {1., 0.}, {2., 0.5}, {2., -0.5}}, {Line[{{1, 2}, {2, 3}, {3, 4}, {4, 2}}]}}

Or

ReleaseHold[MakeExpression[ToBoxes[InputForm[test]][[1, 1]], StandardForm] /. 
  MeshRegion -> List]

{{{0., 0.}, {1., 0.}, {2., 0.5}, {2., -0.5}}, {Line[{{1, 2}, {2, 3}, {3, 4}, {4, 2}}]}}

1 Answers1