Gnuplot: how to plot max and /or min value

Question

How can I show the max. and/or the min. value(s) of of a graph in a plot at their appropriate position automatically?

Answer 1

You can do this "semi-automatically" using the stats command. This command can extract some statistical values from a data set, but requires some reworking:

1. Extract the minimum and maximum y-values, assuming that your data file has two columns, the x-value in the first, the y-values in the second column

   stats 'file.dat' using 2 nooutput name 'Y_'
   

   This gives you the min/max y-values in the variables Y_min and Y_max, but not the corresponding x-value.

2. The previous step gives you only get the respective indices, which requires you to run stats again in order to get the x-values:

    stats 'file.dat' using 1 every ::Y_index_min::Y_index_min nooutput
    X_min = STATS_min
    stats 'file.dat' using 1 every ::Y_index_max::Y_index_max nooutput
    X_max = STATS_max
   

3. Set labels and/or points at the respective coordinates

   set label 1 sprintf("%.2f", Y_min) center at first X_min,Y_min point pt 7 ps 1 offset 0,-1.5
   set label 2 sprintf("%.2f", Y_max) center at first X_max,Y_max point pt 7 ps 1 offset 0,1.5
   ...
   plot ...