Can I use only certain numbers from data file in gnuplot title? - gnuplot

Question

I have a data file with many columns of data and the first two lines look like this:
#time a1 b1 c1 d1 a2 b2 c2 d2
1 2 3 4 5 6 7 8 9
I would like to put a title on the graph which reads like this:
a1=2, a2=6, b1=3, b2=7, c1=4, c2=8, d1=5, d2=9
So, basically just taking the data from the first line and adding some text with it. Is this possible?
Thanks mgilson! Here is the script (the first part.)
#filename = "a6_a.txt"
//defining variables called ofac and residual
unset multiplot
set term aqua enhanced font "Times-Roman,18"
set lmargin 1
set bmargin 1
set tmargin 1
set rmargin 1
set multiplot
set size 0.8,0.37
set origin 0.1,0.08 #bottom
set xlabel "time" offset 0,1 #bottom
set ylabel "{/Symbol w}_i - {/Symbol w}_{i+1}"
set yrange [-pi:pi]
plot filename using 1:(residual($7 -$14)) ti "" pt 1 lc 2, \
"" using 1:(residual($14-$21)) ti "" pt 1 lc 3, \
"" using 1:(residual($21-$28)) ti "" pt 1 lc 4
set origin 0.1,0.36 #mid
set format x "" #mid, turn off x labeling
set xlabel "" #mid
set ylabel "P_{i+1}/P_i" offset 2,0
set yrange [*:*]
plot filename using 1:(($10/ $3)**1.5) ti "P_2/P_1" pt 1 lc 2, \
"" using 1:(($17/$10)**1.5) ti "P_3/P_2" pt 1 lc 3, \
"" using 1:(($24/$17)**1.5) ti "P_4/P_3" pt 1 lc 4
set origin 0.1,0.64 #top
set ylabel "semi-major axes"
set yrange [*:*]
plot filename using 1:($3):($4*$3) with errorbars ti "" pt 1 lc 1, \
"" using 1:($10):($10*$11) with errorbars ti "" pt 1 lc 2, \
"" using 1:($17):($17*$18) with errorbars ti "" pt 1 lc 3, \
"" using 1:($24):($24*$25) with errorbars ti "" pt 1 lc 4
unset multiplot
unset format
unset lmargin
unset bmargin
unset rmargin
unset tmargin

Answer 1

You probably could do this using gnuplot only (I think), but it would be painful. The easiest solution is to write an external script which will format the title for you -- e.g. in python (untested):
#python script formatTitle.py
import sys
fname=sys.argv[1]
with open(fname,'r') as f:
line1=f.readline().split()
line2=f.readline().split()
pairs=sorted(zip(line1,line2)[1:])
print (", ".join("%s=%s"%(p[0],p[1]) for p in pairs))
and then in gnuplot:
set title "`python formatTitle.py datafile.dat`"
EDIT
Your script above has a few problems. First, // is not a comment character in gnuplot -- so that will raise some sort of syntax error right away. Next, you're using filename as a string variable (which is OK) but you've not defined it anywhere. (the first line of your script would probably work except that it has been commented out). Finally, I can't check since I don't have your datafile, but your use of lmargin etc + set size + set origin is a little hard (for me) to track. Someone smarter would probably have no problem with it. When I want to explicitly align my plots however, I use the second form of margin.
#make plots go from 0.1 to 0.9 on the screen (screen range is 0-1)
# (0,0) is the lower left corner, (1,1) is the upper right.
set lmargin at screen 0.1
set rmargin at screen 0.9
And then for each of your sub-plots, you can do:
NPLOTS=3
SCREENSIZE=0.8 #leave .1 for the top and bottom border
DY=SCREENSIZE/NPLOTS #height of each plot
#bottom
set tmargin at screen 0.9-2*DY
set bmargin at screen 0.9-3*DY
#other commands
plot ...
#middle
set tmargin at screen 0.9-DY
set bmargin at screen 0.9-2*DY
#other commands ...
plot ...
#top
set tmargin at screen 0.9
set bmargin at screen 0.9-DY
#other commands ...
plot ...
Of course, you can play around with the positions as you see fit.