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I have a set of data with coordinate and a weight which I map with colours. I want a particular colour to appear on the top of others. For example

c[1] = Blue; c[2] = Red; c[3] = Green;
d1 = {RandomChoice[{1, 2, 3}], RandomReal[1, 2]} & /@ Range[20];
d2 = {RandomChoice[{1, 2, 3}], RandomReal[1, 2]} & /@ Range[20];
Graphics[{{c[#[[1]]], Disk[#[[2]], 0.1]} & /@ d1,
          {c[#[[1]]], Disk[#[[2]], 0.1]} & /@ d2}]

enter image description here

Now I want all the red points to appear on the top layer. Manually I can double-click on each of them and use Move to Front option.

enter image description here enter image description here

Is it possible to do it with a command?

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    $\begingroup$ They are rendered in the order that they appear inside of Graphics. $\endgroup$
    – Szabolcs
    Sep 13, 2017 at 13:16
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    $\begingroup$ FrontEndExecute[FrontEndToken["MoveToFront"]] works. To test the code you can evaluate Button["x",FrontEndExecute[FrontEndToken["MoveToFront"]] ], select the disk, and click on the button. $\endgroup$
    – andre314
    Sep 13, 2017 at 13:39

2 Answers 2

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Assuming your Graphics is saved in a variable g:

c[1] = Blue; c[2] = Red; c[3] = Green;
d1 = {RandomChoice[{1, 2, 3}], RandomReal[1, 2]} & /@ Range[20];
d2 = {RandomChoice[{1, 2, 3}], RandomReal[1, 2]} & /@ Range[20];
g = Graphics[{{c[#[[1]]], Disk[#[[2]], 0.1]} & /@ d1,
          {c[#[[1]]], Disk[#[[2]], 0.1]} & /@ d2}]

graphics

Here is one simple way:

ReplacePart[g, 1 :> SortBy[Flatten[g[[1]], 1], First]]

graphics

A drawback of this approach is that it reorders all the disks, not just puts red disks forward. The following approach only does the latter without reordering:

ReplacePart[g, 
 1 :> {Cases[g[[1]], {Except@Red, _Disk}, -3], Cases[g[[1]], {Red, _Disk}, -3]}]

graphics

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I think the question is (at least partially) answered in a comment by @andre. (That is, use FrontEndExecute[FrontEndToken["MoveToFront"] on selected objects.)

An alternative way, following Alexey's approach, to move primitives with selected color to the front without changing the order of other primitives is to use Pick:

moveToFront[g_, color_: Red] := 
 Module[{prims = Join @@ g[[1]]}, 
  Graphics[Join @@ Pick[prims, #[[1]] === color & /@ prims, #] & /@ {False, True}]]

moveToFront[gr]

enter image description here

moveToFront[gr, Green]

enter image description here

where gr = Graphics[{{c[#[[1]]], Disk[#[[2]], 0.1]} & /@ d1, {c[#[[1]]], Disk[#[[2]], 0.1]} & /@ d2}].

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  • $\begingroup$ Of course, you would need more elaborate selection function in the second argument of Pick for cases where the graphics directives and primitives are organized in arbitrary ways. $\endgroup$
    – kglr
    Sep 13, 2017 at 14:43

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