Variable for data column number?

[Ingo Thies]

Hi all,

I want to plot large data file sequences from computer-generated Gnuplot
scripts. Such a script consists of dozens (or even hundreds) of plot
commands, and the computer-generated script is being loaded from a
driver script via the load command. The data are divided in columns as
usual. I now want to select the columns to be used for plotting by
setting a switch in the driver file.

Normally, data file columns are specified with e.g.

plot 'file' using 1:2

or

plot 'file' using (f($1)):(f($2))

I found that in the former case one could replace the column numbers by
integer variables, e.g.

c1=1;c2=2
plot 'file' using c1:c2

But is it also possible to use variables for column numbers as a
function argument? "$c1" or similar don't work. For now, I can only do
this by replacing the column specifier in all the lines by
search&replace, but a global switch would be much more convenient.

Does anyone have any hints if this can be done?

Ingo

[Juergen Wieferink]

Ingo Thies wrote:
> c1=1;c2=2
> plot 'file' using c1:c2
>
> But is it also possible to use variables for column numbers as a
> function argument? "$c1" or similar don't work. For now, I can only do
> this by replacing the column specifier in all the lines by
> search&replace, but a global switch would be much more convenient.

This could be done using macros "help macro", but the clean way is
via the column() function (help column) [untested]:

c1=1;c2=2
plot 'file' using (column(c1)):(column(c2))

Juergen

[Ingo Thies]

Juergen Wieferink wrote:

> This could be done using macros "help macro", but the clean way is
> via the column() function (help column) [untested]:
>
> c1=1;c2=2
> plot 'file' using (column(c1)):(column(c2))

Ah, this works fine, thanks!

Ingo

[andreas.b...@gmail.com]

Thanks, This works amazing if one wants to do math on each entry in a column, but directly in a bash script, for example subtracting some number from every entry:

#!/bin/bash

gnuplot <<-EOF

set terminal pdf
set output "test.pdf"
plot "data.dat" u 1:(column(2)-2.63E-02) with lines

EOF

evince test.pdf