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I have a matrix which contain rotated ellipses and points, how can I check if the element in the position {i,j} is either a point or an ellipse?

the code is a bit longer but the structure is like:

matrix = table [ if[condition] , Rotate[Circle, parameters[[i,j]]] ,Point [[i,j]],{j,1,900},{i,1,900}]

then I use Graphics over that matrix but I don't want to show the points, that's why i am asking how to detect the points

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  • $\begingroup$ I don't understand the question. It would be best to give an example of such a matrix (a small one, as small as possible while still illustrating the problem) $\endgroup$
    – Szabolcs
    Commented May 28, 2016 at 19:10
  • $\begingroup$ i updated the first post $\endgroup$
    – Alucard
    Commented May 28, 2016 at 19:23

1 Answer 1

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headF1 gets the Head of the expression in the specified part of the matrix. headF2 uses the fact that Part 0 of an expression is its Head.

ClearAll[headF1,headF2]
headF1= Head[#[[## & @@ #2]]] &;
headF2= #[[## & @@ #2]][[0]] &; 

SeedRandom[1]
mat = RandomChoice[{Ellipse[], Point[]}, {5, 3}]

{{Point[], Point[], Ellipse[]}, {Point[], Ellipse[], Ellipse[]}, {Ellipse[], Point[], Ellipse[]}, {Point[], Ellipse[], Ellipse[]}, {Ellipse[], Ellipse[], Ellipse[]}}

headF1[mat, {2, 3}]

Ellipse

headF2[mat, {2, 3}]

Ellipse

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  • $\begingroup$ nvm it works but it gives me Rotate, thanks $\endgroup$
    – Alucard
    Commented May 28, 2016 at 19:25
  • $\begingroup$ can you explain me what the #s do in this case? $\endgroup$
    – Alucard
    Commented May 28, 2016 at 19:29
  • $\begingroup$ @Alucard, you can use headF1[mat, {2, 3}] /. Rotate -> Ellipse. Or change the definition headF1 = Head[#[[## & @@ #2]]]/. Rotate -> Ellipse &. $\endgroup$
    – kglr
    Commented May 28, 2016 at 19:30
  • $\begingroup$ @Alucard, #1, #2 are Slots, used as place-holders for un-named arguments. The pure Function headF1 does the same thing as the function with named arguments headF[ matrix_, part : {_, _}] := Head[matrix[[Sequence @@ part]]]. $\endgroup$
    – kglr
    Commented May 28, 2016 at 19:35
  • $\begingroup$ ok i thought i had solved this but it seems this problem is out of my league. how can i force Graphics to act as i wish upon the matrix ? only the points should be transparent or not elaborated at all $\endgroup$
    – Alucard
    Commented May 28, 2016 at 20:32

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