speeding up Babel Gnuplot

[Thierry Banel <tbanelwebmin@free.fr>]

Babel Gnuplot is quite slow on large tables.
Example: 45 seconds for a 1500 rows table.

Why? Because orgtbl-to-generic is too slow (or too generic). Its
behavior seems to be quadratic O(size^2). Should we bypass it? Should
we try to optimize it?

Here is a fix to speed up the rendering to a mere fraction of a second.

#+BEGIN_SRC elisp
(defun org-babel-gnuplot-table-to-data (table data-file params)
  "Export TABLE to DATA-FILE in a format readable by gnuplot."
  (let ((org-babel-gnuplot-timestamp-fmt
     (or (plist-get params :timefmt) "%Y-%m-%d-%H:%M:%S")))
    (with-temp-file data-file
      (mapc (lambda (line)
          (mapc (lambda (cell)
              (insert (org-babel-gnuplot-quote-tsv-field cell))
              (insert "\t"))
            line)
          (insert "\n"))
        table)))
  data-file)
#+END_SRC

And here is a test case.

First generate a 1500 rows table:

#+BEGIN_SRC elisp :results none
  (goto-char (point-max))
  (insert "#+name: data\n")
  (let ((i 1500))
    (while (> i 0)
      (goto-char (point-max))
      (insert (format "| %4s |\n" i))
      (setq i (1- i))))
#+END_SRC

Then run Babel Gnuplot:

#+BEGIN_SRC gnuplot :var data=data :file x.svg :session none :term svg
plot data
#+END_SRC