Bash, Gnuplot: plot multiple chosen column pairs from one datafile into one plot

Question

I'm making a script to plot desired pairs of columns of a datafile in a window. But i cant figure out how to make gnuplot accept arguments to the using command.

my code looks like this

#!/bin/bash
filee=$1
shift 1
cols=$@

gnuplot -p << eof
#TESTS--------------------------------
print "gnuplot--starts----------------"

print "cols-var is:     $cols"
print "filee-name is:   $filee"

print "pair-vars are:"
do for [pair in "$cols"] {print pair}

print "-------------------------------"
#END TESTS----------------------------"


set term wxt 1 size 1500,900 title 'columns of $filee'
set key top left
set grid
set xrange [2:8]
set yrange [-0.02:0.02]
set format y "%g"
plot for [pair in "$cols"] '$filee' u pair  
eof

If instead of pair as the argument to u i use 1:3 or 1:2 or whatever i get the correct number of plots, but of course they are all identical. I tried a lot of things and everything seem to be working besides that u doesn't accept a variable. The output wher running this is:

$ ./cploter written.dat 1:2 1:3 1:4
gnuplot--starts----------------
cols-var is:    1:2 1:3 1:4
filee-name is:  written.dat
pair-vars are:
1:2
1:3
1:4
-------------------------------
         line 0: warning: Skipping data file with no valid points
         line 0: warning: Skipping data file with no valid points
         line 0: warning: Skipping data file with no valid points

Some help with this issue would be appreciated:)

EDIT: as u doesn't seem to be accepting the loop through its arguments I settled for the code below. If You know a different approach to plot desired column pairs into one plot, please leave a comment or answer:)

#!/bin/bash
fil=$1; xx=$2; y1=$3; y2=$4
gnuplot -p <<- eof
set term wxt 1 size 1500,900 title 'columns of $filee'
set key top left
set format y "%g"
plot for [i=${y1}:${y2}] '$fil' u ${xx}:i w l t 'Column ${xx}:'.i
eof

I'm on gnuplot 4.6. using for [i in $range] does not work in this case for some reason. Using variables ys(i)=word("$yes",i), xs=word("$xes",i) and plot for [i=1:3] '$fil' u xs(i):ys(i) w l doesn't work either.

andyras · Accepted Answer · 2015-02-05 16:07:29Z

1

(Partial answer; there are a few other ways of working around this situation)

I get a different error running your script (gnuplot 5.0)

line 0: warning: no column with header "1:2"

but I think the source of the problem is the same. The issue is that gnuplot is looking for a single column with the name "1:2" rather than interpreting the token "1:2" as a two-column using specification.

If you only want to plot pairs of the form 1:2, you can just pass the second column indices as arguments to your script and use the plot command

plot for [pair in "$cols"] '$filee' u 1:column(int(pair))

edited Feb 5, 2015 at 16:07

answered Feb 4, 2015 at 17:32

andyras

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4 Comments

Christoph Over a year ago

I think you must use using 1:(column(pair)).

andyras Over a year ago

@Christoph, I tried that as well and it did not work properly. It acts as if I had issued columnhead(pair) and gives an error line 0: warning: no column with header "3", for example.

Christoph Over a year ago

You are right, column(p) checks the data type of variable p: if it is a string, it is used as column label to select a column. Otherwise it is used a column index. A value of "3" isn't casted to int. You must do this yourself with using 1:(column(int(pair))).

Jonatan Öström Over a year ago

I kind of settled for this kind of structure, see the updated post. Thanks anyway. If you come up with something, please post it. Sadly the `[pair in "$cols"] is not working at all.

Christoph · Accepted Answer · 2015-02-05 10:28:08Z

0

Using [pair in "$cols"] works fine, provided all the rest is also correct. The following example works fine:

File test.dat

1 2 3 4
5 6 7 8
9 10 11 12

and the script plot.sh:

#!/bin/bash
filee=$1
shift 1
cols=$@

gnuplot -p <<EOF
set terminal pngcairo
set output 'test.png'
plot for [col in "$cols"] '$filee' u 1:(column(int(col)))

EOF

Call this script with

./plot.sh test.dat 2 3 4

answered Feb 5, 2015 at 10:28

Christoph

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