Re: [PATCH] Makes sort create random order

[Thomas Habets]

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Once upon a midnight dreary, Jim Meyering pondered, weak and weary:
>   sort: Add an ordering option -R that causes 'sort' to sort according
>     to a random permutation of the correct sort order.

This means that two different files, that happen to sort to the same output,
should give the same output when randomized with the same SEED. Is that
right? 

I'm not a sorting-expert, but this would mean running through the input twice,
would it not? Once to get the common input, and then another to randomize it.

Is there a good reason for wanting this? It can be emulated by piping it 
through sort before randomizing it. Getting different results can not be 
emulated, however.

>     if you sort a permutation of the same input file
>     with the same --random-seed=SEED option twice, you'll get the same
>     output.

Here however it does not explicitly say what I said above about two different
files.

>     The default SEED is chosen at random, and contains enough
>     information to ensure that the output permutation is random.

So what is "random"? Do we mean "arbitrary" or "unpredictable"?
Also, should "deteministic" here mean that it should now, and forever, and on
all architectures, work the same?

If the latter, and especially if the former, then some thinking will have to
go into it.

But except for writing the PRNG, everything else is trivial. :-)

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