How set point type from data in gnuplot?

Question

How set point type from data in gnuplot?

gnuplot script:

set terminal pngcairo size 640,480
set output "points.png" 
set style data points 
set auto x 
set autoscale x 
unset colorbox 
plot 'test.data' using 2:1 with points notitle

test.data

32  35  8
34  34  6
36  28  1
34  32  2
28  30  7
38  30  9
34  29  2
35  36  9
39  34  3
31  33  9
28  31  6
35  30  5
33  41  4
32  37  3

how get point type from 3 column?

plot 'gnuplot.data' using 2:1 with points pt (:3) notitle // error 

abstraction example:

need:

gnuplot Version 4.6 patchlevel 4

Answer 1

There is no option to select the point type from the data file based on a column (equivalent to linecolor variable, pointsize variable or arrowstyle variable). Basically you have two options:

1. Iterate over all possible point types (which you can extract with stats if this should be variable) and for each number plot only those points which match the current point type:

   stats 'test.data' using 3 nooutput
   unset key
   set style data points
   plot for [i=STATS_min:STATS_max] 'test.data' using 2:($3 == i ? $1 : 1/0) lt 1 pt i ps 2
   

2. Use the labels plotting style and a sequence of unicode point symbols from which you select using the value from the third column as index. (use e.g. http://www.shapecatcher.com or http://decodeunicode.org/en/geometric_shapes to find suitable symbols)

   unset key
   set encoding utf8
   symbol(z) = "•✷+△♠□♣♥♦"[int(z):int(z)]
   plot 'test.data' using 2:1:(symbol($3)) with labels textcolor lt 1