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graphics - ListPlot with conditions


I have a data file containing the position of about 105 stars of a spiral galaxy. Here is the plot


enter image description here


and this is the corresponding code


Clear["Global`*"]
SetDirectory[" ... "];


data = Import["data_SGC.out", "Table"];
L0 = ListPlot[data, PlotStyle -> {Blue, PointSize[0.001]}, Axes -> False, 
              Frame -> True, FrameLabel -> {"x", "y"}, 
              RotateLabel -> False, LabelStyle -> Directive[FontFamily -> "Helvetica", 20], 
              AspectRatio -> 1, PlotRange -> 100, ImageSize -> 550];

As we can see, there are two arms starting at about (x,y)=(−14.6,0) and (x,y)=(14.6,0). Now I would like to customize ListPLot, so as the arm starting at the left part (x,y)=(−14.6,0), be in green color, while the other one in red. All the other points between the two yellow banana-type areas should be in gray.


Any suggestions?


The complete data file can be found here: data. Obviously, I could not generate simple random data in order to replicate this complicated spiral structure.




Answer



You have somehow to segment your data. Here you could use the radius + FindClusters:


    radius = 14.6;
    data1 = FindClusters[Select[data, Norm[#] > radius &], 2,Method -> "Agglomerate"];
    Show[
      ListPlot[data1, PlotRange -> Full, AspectRatio -> 1, PlotStyle -> {Green, Red}],
     ListPlot[Select[data, Norm[#] < radius &], PlotRange -> Full, AspectRatio -> 1, PlotStyle -> Gray]
    ]

This will give you something like this:



enter image description here


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