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Let's say I have a listplot like so:

ListPlot[Prime[Range[25]]]

I want my plot to mark the x,y values for the values associated with say, the 5th, and 10th points in the input. I would be interested in any of the following:

  • marking simply the y values so have 11 and 29 in the y axis
  • marking both x and y axis: ie show {5,11} and {10,29} in the x and y axis respectively.

with, or without perpendicular lines connecting the points to axes.

The point of this, is to give the reader of the plot, a sense of scale for given points of interest.

Do I have to superimpose different plots on each other or can I do it by some config on the listplot itself?

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  • $\begingroup$ Use Ticks ? For example: ListPlot[Prime[Range[25]], Ticks -> {{5, 10}, Prime[{5, 10}]}, Epilog -> {Gray, Dashed, Line[{{5, 0}, {5, Prime[5]}}], Line[{{10, 0}, {10, Prime[10]}}], Line[{{0, Prime[5]}, {5, Prime[5]}}], Line[{{0, Prime[10]}, {10, Prime[10]}}] }] $\endgroup$
    – flinty
    Jul 15, 2020 at 22:28
  • $\begingroup$ ah! how did I miss that! yeah that would do the trick :) $\endgroup$
    – Shb
    Jul 15, 2020 at 22:31
  • 2
    $\begingroup$ This is a bit more general: With[{points = {5, 10, 13}}, ListPlot[Prime[Range[25]], Ticks -> {points, Prime[points]}, Epilog -> {Gray, Dashed, {Line[{{#, 0}, {#, Prime[#]}}], Line[{{0, Prime[#]}, {#, Prime[#]}}]} & /@ points }]] $\endgroup$
    – flinty
    Jul 15, 2020 at 22:31
  • $\begingroup$ @flinty little improvement on this ^ mathematica.stackexchange.com/a/226205/8988 $\endgroup$
    – Shb
    Jul 19, 2020 at 18:22

1 Answer 1

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This is a more readable and reusable version of the suggestion by @fliny

With[
  {
    points = Table[{n,Fibonacci[n]}, {n, 7}],
    sampleValues = {1,5,7}
  },
  ListPlot[
    points,
    Joined -> True,
    Ticks -> {sampleValues , points[[All,2]][[sampleValues]]},
    Epilog -> {
      Dashed,
      {
        Line[{Projection[points[[#]], {1,0}], points[[#]]}], (*X-axis projection*)
        Line[{Projection[points[[#]], {0,1}], points[[#]]}]  (*Y-axis projection*)
      } & /@ sampleValues
    }
  ]
]

it will produce the following:

enter image description here

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