How to make a spider plot in gnuplot?

Question

Let's say my data is in the form:

#atom a b c
43 1.2 1.3 1.4
44 1.2 1.4 1.8
45 1.3 1.8 1.9
46 2.0 2.3 2.4
47 1.5 1.6 1.8

And I want a plot like this one http://www.r-graph-gallery.com/143-spider-chart-with-saveral-individuals/ (the one in the middle).

how can I do that?

ps. The title in here (How to Create a Spider Plot in Gnuplot?) is misleading...

Answer 1

As far as I know, there is no built-in functionality which would directly give you the linked output. Nevertheless, one could improvise with the tools that Gnuplot does provide. The strategy would be to:

1. analyze the file and determine the number of vertices
2. generate the "polygonial" grid in parametric mode
3. plot the data using the filledcurves plotting style (with transparency)

For example (the data is represented as a datablock instead of directly passing a file):

reset session
set terminal pngcairo enhanced font "Times,16"
set output 'plot.png'

$DATA << EOD
#atom a b c
43 1.2 1.3 1.4
44 1.2 1.4 1.8
45 1.3 1.8 1.9
46 2.0 2.3 2.4
47 1.5 1.6 1.8
EOD

stats $DATA nooutput

N = STATS_columns
M = STATS_records

set angles degrees
set size ratio -1
set style fill transparent solid 0.25

unset key
unset border
unset xtics
unset ytics

colors = "dark-red royalblue forest-green"

set style line 42 lt 1 lc rgb '#333333' dt 3 lw 0.8

deltaR = 0.5
maxR = 3 + deltaR/4
numOfStepsInR = floor((1.*maxR) / deltaR)

#helper functions
alpha(i) = 90. - i*360./M
posX(i, r) = cos(alpha(i))*r
posY(i, r) = sin(alpha(i))*r
lcolor(i) = word(colors, i%words(colors) + 1)

do for [i=0:M-1] {
  stats $DATA every ::i::i using (labelValue=$1) nooutput
  set label sprintf("%d", labelValue) at posX(i,maxR),posY(i,maxR) center offset char posX(i,1),char posY(i,1)
}

do for [j=1:numOfStepsInR] {
  set label sprintf("%.1f", j*deltaR) at 0,j*deltaR left offset char 0.5,0 tc rgb '#333333'
}

set parametric
set tr [0:1]

set xr [-1.1*maxR:1.1*maxR]
set yr [-1.1*maxR:1.1*maxR]

plot \
  for [i=0:M-1] \
    (cos(alpha(i))*(deltaR*(1-t)+t*maxR)),(sin(alpha(i))*(deltaR*(1-t)+t*maxR)) w l ls 42, \
  for [i=0:M-1] for [j=1:numOfStepsInR] \
    (j*deltaR*cos(alpha(i))*t + (1-t)*j*deltaR*cos(alpha(i+1))),(j*deltaR*sin(alpha(i))*t + (1-t)*j*deltaR*sin(alpha(i+1))) w l ls 42, \
  for [i=2:N] $DATA u (posX($0, column(i))):(posY($0, column(i))) w filledcurves closed fc rgb lcolor(i-2) fs border lc rgb lcolor(i-2) lw 2, \
  for [i=2:N] $DATA u (posX($0, column(i))):(posY($0, column(i))) w p ps 1.2 pt 7 lc rgb lcolor(i-2)

This produces: