Plot from two files with errorbars for Gnuplot

Question

I am thinking which way to do the addition of errorbars better by thinking the format of data. The standard way of adding errors bars is discussed here, for instance.

Answer 1

First of all, I wonder about your columns used for plotting with yerrorlines. If your first data for 2025 is 75.5+/-2.5, you usually plot it with

plot "datafile" using <xcolum>:<ycolum>:<yerrorcolumn>

Your six columns are for the case of xy errorbars and specify the point itself and the lower and upper absolute values in x and y. But may be you are just doing it as you need it...

Now back to your question: Gnuplot can not handle data from two files simultaneously, i.e. it can not take xy-values from one file and y-errors from another.

If you're running linux, the command line tool join can help. Your averages stored in file A and the errors in file B, join A B will concatenate lines with the same value in the first colum like this:

2025 75.5 82.5 89.5 2.5 2.5 2.5

So,

plot "<join A B" using 1:2:5 with yerrorlines

should do the job. ("<join A B" will call the join command in the background and read its output like a data file)

Answer 2

Gnuplot 5 supports that you specify several characters as data file separators.

So, if you are sure you'll never get negative values (which I hopen given the format of your data), then you can use your original data file and set both white space and hyphen as datafile separator:

set datafile separator " -"
plot for [i=2:6:2] "data" using 1:(0.5*(column(i)+column(i+1))):(0.5*(column(i+1)-column(i))) with yerrorlines