How to skip missing data in gnuplot

Question

I have the following data:

1  2  3  4
1  2  3  4
1  2     4
1  2     4

If I use

plot "file" u 1:3

then it plots {1,3},{1,3},{1,4},{1,4}

How do I plot it following the column?

This is a txt file.

Answer 1

gnuplot's standard column separator is whitespace and does not distinguish between a single space and multiple spaces. Check help datafile separator. If your column separator is strictly one and only one space you can simply set datafile separator " ".

However, then your data must look like this:

1 2.1 3.1 4.1
2 2.2 3.2 4.2
3 2.3  4.3      # two spaces but not more
4 2.4  4.4      # ditto
5 2.5 3.5 4.5

But since your data doesn't seem to look like this, you probably have to go for this workaround.

Nevertheless, here is the first option.

Script:

### empty columns
reset session

$Data <<EOD
1 2.1 3.1 4.1
2 2.2 3.2 4.2
3 2.3  4.3
4 2.4  4.4
5 2.5 3.5 4.5
EOD

set key out tmargin

set multiplot layout 1,2

    set datafile separator whitespace    # this is default
    plot $Data u 1:2 w lp pt 7 lc "red", \
           ''  u 1:3 w lp pt 7 lc "green", \
           ''  u 1:4 w lp pt 7 lc "blue"

    set datafile separator " "
    plot $Data u 1:2 w lp pt 7 lc "red", \
           ''  u 1:3 w lp pt 7 lc "green", \
           ''  u 1:4 w lp pt 7 lc "blue"

unset multiplot
### end of script

Result: