Re: Random number generation in LISP or using it

[Xah Lee <xahlee@gmail.com>]

On Jun 10, 8:21 am, bolega <gnuist...@gmail.com> wrote:
> I am a newbie with the following problem.
>
> A the outset let me state that the limitation is that I have to use
> this inside emacs to scramble a set of chosen lines like you do
> "reverse-region" or "sort-lines". It is possible that I can call some
> scheme or clisp functions.
>
> What is a fast(est) method to randomize lines based on the
> capabilities of emacs ?
>
> The function "random" does not work in emacs. I guess one get the
> start line and end line of a marked region and then use that to
> disorder (or re-order) the lines according to a list of random numbers
> generated ?
>
> 1 -> 5
> 2 -> 8
> 3 -> 6
> 4 -> 9
> 5 -> 1
> 6 -> 3
> 7 -> 2
> 8 -> 7
> 9 -> 4
>
> and then use these pairs to reorder the lines. I guess there is a need
> for one or two variables to hold the lines, or just a kill or the top
> line and go down a certain number of random steps and paste it there ?
> Then come back to the top and do the same thing. The type of capacity
> I am looking is to randomize about few hundred short lines of about 20
> to 30 characters.
>
> In this case one needs to generate a random number that is an integer
> and lies between the lines start and end of region. It can be done by
> some modulo type operation if available in emacs lisp.
>
> Thanks for any help.
> gnuist

your problem is very easily solved, in fact i have code you can mode a
bit to do exactly what you want.

The simplest solution, for your input size, is simply just to grab
your lines and save as list. Then, randomnize the list, then insert
them one by one. Probably a 20 min job.

i assume you know scheme or common lisp, just not familiar with emacs
lisp features.

To get your lines into list, as a example, see the grab-lines function
here:

• Elisp Lesson: Writing a google-earth Function
  http://xahlee.org/emacs/google-earth.html

or you can see this page, that deals with reading lines one at a time.

• How To Process A File Line By Line In Elisp
  http://xahlee.org/emacs/elisp_process_lines.html

basically, i'd just do this:

• move your cursor to beginning of first line. (Use search-backward on
\n\n.)
• Move your cursor to the beginning of first line. (move-beginning-of-
line)
• save cursor pos as pos1.
• move your cursor to end of line. move-end-of-line
• save cursor pos as pos2.
• use buffer-substring-no-properties to grab the line and push into a
list.
• Repeat above.
• Delete the lines in buffer if you haven't already.
• Once you have lines as a list, call random with list length as arg.
• remove that line from your list and insert into buffer.
• Repeat till you list has length 0.

  Xah
∑ http://xahlee.org/

☄