Re: [Gnuplot-info] Storing point from data file in variable

[Thomas S. <t.s...@fz...>]

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


Jeremy Conlin wrote:
> 
> On Thu, Jun 4, 2009 at 5:06 AM, Thomas Sefzick
> <t.s...@fz...>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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