Use a single record of a file with multiple columns in gnuplot

Question

Let's say I have the following data stored in the file 'file' (exciting!):

a_0 a_1 a_2 a_3
b_0 b_1 b_2 b_3
...

and also a given function f. I want to draw several plots, one after the other, each consisting of a single point in (x,y) coordinates : a_2,f(a_2), then b_2,f(b_2), etc.

I want to use a gnuplot-only solution (and I think there must be one, although I can't find it !).

I am looking for something like :

plot 'file' every ::0::0: using ($2):(f($2))
pause -1
plot 'file' every ::1::1: using ($2):(f($2))
...

I seem to be doing something too complicated... Thanks for any help !

The column numbers start at 1, 0 is the row number. So with plot 'file' every ::0::0 using 3:(f($3)) it should work fine. — Christoph
– Christoph, Commented Mar 24, 2014 at 22:28
Yes you're right Christoph. But it's a typo I made ! Your suggestion doesn't work either. — bela83
– bela83, Commented Mar 25, 2014 at 6:33
Yes, I understood that. And I don't see the problem or error you're having with it. See my answer for a working example. — Christoph
– Christoph, Commented Mar 25, 2014 at 7:34

Christoph · Accepted Answer · 2014-03-25 07:33:49Z

2

The following works fine for me. Take a data file file:

0 1 2 3 4 
5 6 7 8 9

And then use:

f(x) = x**2
plot 'file' every ::0::0 using 3:(f($3))

That plots me a single point at (2, 4). For an automatic iteration use e.g.

stats 'file' using 0 nooutput
do for [i=0:int(STATS_records-1)] {
    plot 'file' every ::i::i using 3:(f($3))
    pause -1
}

answered Mar 25, 2014 at 7:33

Christoph

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13 Comments

bela83 Over a year ago

Dear Christoph, it works now ! I removed the ':' at the end, i.e. what works is 'every ::0::0' as you stated and NOT 'every ::0::0:' as I had previously tried. Do you know why ?

Christoph Over a year ago

I haven't noticed that semicolon at the end. I guess its a limitation of the parsing of the every expression which doesn't allow an ending semicolon. However, this is either a bug in the parsing, or the documenation must be adapted, which currently says: Any of the numbers can be omitted; the increments default to unity... (see help every). But I do also get an error with every ::0::0:, undefined variable using, didn't you get one, too?

bela83 Over a year ago

With every ::0::0:1 it is OK for me. Is that what you meant ? With every ::0::0: I get the error undefined variable using. I use Gnuplot on a remote machine with version 4.4 patchlevel 2. I agree with your remark on the documentation, as it was my source for my line of code !!

Christoph Over a year ago

Yes, that's what I meant. I'll report that to the gnuplot developers.

bela83 Over a year ago

Thanks Christoph. As a matter of fact, my complete command is plot 'file' every ::0::0 using 3:(f($3)),f(x) and I got the following message empty x range [2:2], adjusting to [1.98:2.02] so that I don't get any relevant information for the whole function f... Do you know why Gnuplot does that ?

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