Re: avoid narrow-to-region (was: Re: replace-regexp)

[Yuri Khan <yuri.v.khan@gmail.com>]

On Sun, 9 May 2021 at 13:10, Emanuel Berg via Users list for the GNU
Emacs text editor <help-gnu-emacs@gnu.org> wrote:

> > * Consistency: If (f a b) returns t once, it must return
> > t when called again with the same arguments. [...]
>
> But here, we want to randomize _every time_.

Every time you do a random shuffle, but not within a single shuffle.

A theoretically sound (but still unnecessarily slow) sorting-based
shuffle would first assign a random weight to each line, and then sort
by that weight.

But contrast with this:

* Count the lines to be shuffled. Call it N.
* Generate a random number K_1 from 1 to N. Swap line 1 with line K_1.
* Generate a random number K_2 from 2 to N. Swap line 2 with line K_2.
…
* Generate a random number K_{N-1} from N-1 to N. Swap line N-1 with
line K_{N-1}.

Almost easy enough to put in Elisp, and guarantees uniform
distribution (as long as individual random indexes are uniformly
distributed).