gnuplot from stdin twice

Question

I would like to re-use the same stdin data for two or more lines in code like

plot '-' using 0:1 with lines, '' using 0:1:2 with yerrorbars
3.4 0.1
2.9 0.2
8.8 0.5
2.1 0.7

This code would work if instead of stdin I store all data into a file and then plot from this data file. However, plotting from stdin, the code behaves exactly like

plot '-' using 0:1 with lines, '-' using 0:1:2 with yerrorbars
3.4 0.1
2.9 0.2
8.8 0.5
2.1 0.7

(i.e. '-' instead of '') and gives a warning “Skipping data file with no valid points” instead of printing error bars to the line-plotted data.

Obviously, the plot can be made to work if I duplicate the data on stdin

plot '-' using 0:1 with lines, '' using 0:1:2 with yerrorbars
3.4 0.1
2.9 0.2
8.8 0.5
2.1 0.7
e
3.4 0.1
2.9 0.2
8.8 0.5
2.1 0.7

but I find this unsatisfactory, because then "" means the same thing as "-" for stdin. Of course, what I am looking for would require gnuplot to silently store the most recent data segment from stdin for potential re-use, which is probably in most cases not necessary. Still I do not think it is a huge burden on efficiency. So perhaps there is an option or a different use of gnuplot syntax that I do not know?

I do not know why I did not find them in the first search, but here are closely related questions: stackoverflow.com/questions/28921556/… and stackoverflow.com/questions/4585770/… in case anybody has the same problem. — Bernhard Bodenstorfer
You could combine stdin and datablock with table. See help plot with table. — GRSousaJr

theozh theozh · Accepted Answer · 2019-10-29T07:28:53

Why not using a datablock? I never use '-', exactly because of this issue. You can clear the data with undef $Data. Check help datablocks and help undef.

Code:

### re-use of data from a datablock 
reset session

$Data <<EOD
3.4 0.1
2.9 0.2
8.8 0.5
2.1 0.7
EOD

set xrange [-0.2:3.2]
plot $Data u 0:1 w l, '' using 0:1:2 w yerrorbars
### end of code

Result:

gnuplot from stdin twice

1 Answers