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Re: Storing point from data file in variable
by Thomas Sefzick
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starting with gnuplot 4.3-cvs there are new operators
'=' and ',' in expression syntax, that means, one can use
them for the 'using' modifier inside a 'plot' command.
defining labels must be done before plotting, but access
to the data you don't have before plotting, so filling a variable
with some value from the datafile can only be done
when plotting (but then it's too late to define a label).
one solution is to do a dummy plot by plot 'nothing to
nowhere', by doing this you can set the variable.
(plotting to nowhere can be done by specifying
'set out "/dev/null"' on unix systems, or, plotting
nothing can be done by printing a table to
the terminal window or text window)
then you define the title, label, ....
and afterwards you do the real plot.
gnuplot> set table
gnuplot> plot 'datafilename' us 0:($0==0?(x1=$3):$3)
gnuplot> unset table
for explanation of the syntax see
gnuplot> help table
gnuplot> help ternary
gnuplot> help using
gnuplot> help using pseudocolumns
'=' and ',' in expression syntax, that means, one can use
them for the 'using' modifier inside a 'plot' command.
defining labels must be done before plotting, but access
to the data you don't have before plotting, so filling a variable
with some value from the datafile can only be done
when plotting (but then it's too late to define a label).
one solution is to do a dummy plot by plot 'nothing to
nowhere', by doing this you can set the variable.
(plotting to nowhere can be done by specifying
'set out "/dev/null"' on unix systems, or, plotting
nothing can be done by printing a table to
the terminal window or text window)
then you define the title, label, ....
and afterwards you do the real plot.
gnuplot> set table
gnuplot> plot 'datafilename' us 0:($0==0?(x1=$3):$3)
gnuplot> unset table
for explanation of the syntax see
gnuplot> help table
gnuplot> help ternary
gnuplot> help using
gnuplot> help using pseudocolumns
Jeremy Conlin wrote:On Thu, Jun 4, 2009 at 5:06 AM, Thomas Sefzick <t.sefzick@fz-juelich.de>wrote:
>
> get 1st data of column 3:
>
> x1 = system("head -n1 datafilename | cut -d ' ' -f 3")
> or
> x1 = system("head -n1 ts.dat | awk '{print $3}'")
>
> or with gnuplot 4.3-cvs:
>
> set table
> plot 'datafilename' us 0:($0==0?(x1=$3):$3)
> unset table
>
I do have gnuplot 4.3 and that command sets x1 to the value I want. But
it's rather cryptic. Can you tell me what everything means or point me
toward the documentation explaining it?
Thanks,
Jeremy
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