feedgnuplot: labelled bar charts and a guide

I've thought about adding these for a while, but had no specific need for them. Finally, somebody asked for it, and I wrote the code. Now that I can, I will probably use these all the time. The new capability can override the usual numerical tic labels on the x axis, and instead use text from a column in the data stream.

The most obvious use case is labelled bar graphs:

echo "# label value
      aaa     2
      bbb     3
      ccc     5
      ddd     2" | \
feedgnuplot --vnl \
            --xticlabels \
            --with 'boxes fill solid border lt -1' \
            --ymin 0 --unset grid

But the usage is completely generic. All --xticlabels does, is to accept a data column as labels for the x-axis tics. Everything else that's supported by feedgnuplot and gnuplot works as before. For instance, I can give a domain, and use a style that takes y values and a color:

echo "# x label y color
        5 aaa   2 1
        6 bbb   3 2
       10 ccc   5 4
       11 ddd   2 1" | \
feedgnuplot --vnl --domain \
            --xticlabels \
            --tuplesizeall 3 \
            --with 'points pt 7 ps 2 palette' \
            --xmin 4 --xmax 12 \
            --ymin 0 --ymax 6 \
            --unset grid

And we can use gnuplot's support for clustered histograms:

echo "# x label a b
        5 aaa   2 1
        6 bbb   3 2
       10 ccc   5 4
       11 ddd   2 1" | \
vnl-filter -p label,a,b | \
feedgnuplot --vnl \
            --xticlabels \
            --set 'style data histogram' \
            --set 'style histogram cluster gap 2' \
            --set 'style fill solid border lt -1' \
            --autolegend \
            --ymin 0 --unset grid

Or we can stack the bars on top of one another:

echo "# x label a b
        5 aaa   2 1
        6 bbb   3 2
       10 ccc   5 4
       11 ddd   2 1" | \
vnl-filter -p label,a,b | \
feedgnuplot --vnl \
            --xticlabels \
            --set 'style data histogram' \
            --set 'style histogram rowstacked' \
            --set 'boxwidth 0.8' \
            --set 'style fill solid border lt -1' \
            --autolegend \
            --ymin 0 --unset grid

This is gnuplot's "row stacking". It also supports "column stacking", which effectively transposes the data, and it's not obvious to me that makes sense in the context of feedgnuplot. Similarly, it can label y and/or z axes; I can't think of a specific use case, so I don't have a realistic usage in mind, and I don't support that yet. If anybody can think of a use case, email me.

Notes and limitations:

• Since with --domain you can pass in both an x value and a tic label, it is possible to give it conflicting tic labels for the same x value. gnuplot itself has this problem too, and it just takes the last label it has for a given x. This is probably good-enough.
• feedgnuplot uses whitespace-separated columns with no escape mechanism, so the field labels cannot have whitespace in it. Fixing this is probably not worth the effort.
• These tic labels do not count towards the tuplesize
• I really need to add a similar feature to gnuplotlib. This will happen when I need it or when somebody asks for it, whichever comes first.

This fills in a sorely needed missing part of the documentation: the main feedgnuplot website now has a page containing examples and corresponding graphical output. This serves as a tutorial and a gallery demonstrating some usages. It's somewhat incomplete, since it can't show streaming plots, or real-world interfacing with stuff that produces data: some of those usages remain the the README. It's a million times better than what I had before though, which was nothing.

Internally this is done just like the gnuplotlib guide: the thing is an org-mode document with org-babel snippets that are evaluated by emacs to make the images. There's some fancy emacs lisp to tie it all together. Works great!