Plotting the difference of two columns in the same file

Question

I have a file with 12 columns. I'd like to plot the data with x axis being my 1st column and y axis being the difference between the 2nd and the 8th columns.

I tried plot "test.dat" using 1:(8-2) but naturally, it is interpreted as 1:6. How can I do this?

Answer 1

You are missing $, just add them and they will allow you to reference the column contents

plot "test.dat" using 1:($8-$2) w linespoints

$1 is a shortcut for column(1) and if the column numbers are stored in variables i and j you must use the column statement to select the respective columns:

i = 8
j = 2
plot "test.dat" using 1:(column(i)-column(j)) w lp