Plotting data sequentially from emacs using Common Lisp and Gnuplot

Question

Assume that I have some array of data (a vector to be specific). Can I plot it element by element sequentially using Gnuplot such that it seems as if it is a real life signal that is being traced through a monitor?

I know that I can write the whole data into a text file using Common Lisp, then using gnuplot I can plot it in a batch format. What I require is that I want to put a point on my plot as data comes sequentially.

Data will probably be generated inside a loop, thus you may consider x-axis as the integer valued discrete-time axis. So in the loop if the first element of the array is generated as 5, I would like to put a point on my plot to (0,5). Then if the second element is generated as 3, I would like to put another point on my plot to (1,7) (preserving the old data point). So as I iterate through the loop, I plot the data sequentially.

I am using emacs and Common Lisp for my purposes and I want to plot this data staying within these tools. If there are any other options other than Gnuplot, I would like to hear them.

If this is not easily possible, it would be cool, if I can run a Gnuplot command file by some Common Lisp command.

edit:

Following advices people gave under this thread, I wrote a code using cgn which uses ltk.
Right now I open two x11 windows at pre-specified positions on my screen and I enter the loop. In loop each time I open a stream and write the data (sine and cosine waves of 0.25 Hz sampled at 20 Hz) to the text file trial.txt with the :if-exists :append option and close the stream. Then at each iteration I plot the whole data using the gnuplot through the format-gnuplot command. This code gives me two windows of pre-specified x and y ranges and then one can watch the evolutions of aforementioned sine and cosine waves in the windows.
As I have stated before I don't have strong programming background (I am an electrical engineer who somehow ended using common lisp) and I am pretty sure that my code is non-optimal and unelegant. If you guys have some further advices, corrections etc. I would really like to hear them. The code is here:

(setf filename "trial.txt")
(setf path (make-pathname :name filename))
(setf str (open path :direction :output  :if-exists :supersede :if-does-not-exist :create))
(format str "~,4F ~,4F" -1 -1)
(close str)

;start gnuplot process
(start-gnuplot "/Applications/Gnuplot.app/Contents/Resources/bin/gnuplot")

;set 2 x11 windows with the following properties
(format-gnuplot "cd ~S" "Users/yberol/Desktop/lispbox/code")
(format-gnuplot "set terminal x11 0 position 0,0")
(format-gnuplot "set xrange [0:10]")
(format-gnuplot "set yrange [-1:1]")
(format-gnuplot "unset key")
(format-gnuplot "set grid")

(format-gnuplot "plot ~S using 1" filename)
(format-gnuplot "set terminal x11 1 position 800,0")
(format-gnuplot "plot ~S using 2" filename) 

;write data into text 
(loop :for i :from 0 :to 10 :by (/ 1 20) :do
   (setf str (open path :direction :output  :if-exists :append :if-does-not-exist :create))
   (format str "~,4F ~,4F ~,4F ~%" i (sin (* 2 pi (/ 5 20) i)) (cos (* 2 pi (/ 5 20) i)))
   (close str)
   (format-gnuplot "set terminal x11 0")
   (format-gnuplot "plot ~S using 1:2 with lines" filename)
   (format-gnuplot "set terminal x11 1")
   (format-gnuplot "plot ~S using 1:3 with lines" filename)
   (sleep 0.1))
(close-gnuplot)

Thank you very much.

Answer 1

cgn is a working Common Lisp solution for interfacing with gnuplot, which uses LTK

Answer 2

You could create process to gnuplot and send data to it's stdin along with plotting commands. I'm not sure how to manage such process in Common Lisp but you definitely can do this in Emacs:

(setf *gnuplot-proc* (start-process "gnuplot" "*gnuplot-proc*" "gnuplot"))
;;; initiate plotting of data from stdin
(process-send-string *gnuplot-proc*
                     "plot \"-\" with lines\n")
;; send your data
(process-send-string *gnuplot-proc*
                     "5 -1\n4 -3.5\n3 9.5\n")
;; end of data, after this gnuplot would pop up interactive window
(process-send-string *gnuplot-proc* "e\n")

With such asynchronous process it's easy to write something to make it interactively update plot as new data comes along.

Answer 3

You might have a look at the orgplot mode, which ties gnuplot into emacs org tables.

http://orgmode.org/worg/org-tutorials/org-plot.html