randomly order a list

[Dar Scott]

I tinkered with the same thing.

I also made a random generator using md5 with the long seconds as the seed.  In that, md5 is applied to previous result, not each, requiring a separate function, but each can be mixed in.  

I assume there is nothing weird in a text sort that will affect this.  I assume ignoring case (if that is done) will not affect results, but I really don't know.

I don't really know the properties of any of these (digests are not made to be randomizers), but I think all have the merits mentioned and the caveats noted.

Dar


On Jun 4, 2013, at 11:51 AM, Geoff Canyon wrote:

> At the risk of beating the decaying equus -- the previously suggested
> random() solutions should be fine for all purposes --I found an alternative
> that:
> 
> 1. Is faster than sorting by random(999999999) & random(999999999)
> 2. Is about as fast as sorting by random(999999999)
> 3. Is (I think) less likely to have duplicate sort keys
> 
> The drawback is that it is determinative (albeit random) for any given set
> of data, unless you are willing to accept performance equivalent to sorting
> by random(999999999) & random(999999999), while providing near-certainty of
> a true sort (I think).
> 
> The one-time, as fast as any solution so far, sort is:
> 
>      sort lines of myVar by md5digest(each)
> 
> Collisions are highly unlikely in 128 bits. Even random(999999999) &
> random(999999999) only provides about 60 bits, which, to be clear, is
> *more* than enough, but md5 is (I think) even more certain, and faster.
> However, it will always produce the same results.
> 
>      sort lines of myVar by sha1digest(each)
> 
> Works roughly the same: 160 bits of guaranteed-no-collision-ness, but it's
> a little slower, although still much faster than random(999999999) &
> random(999999999). Like MD5, it will always sort the same data the same
> (random) way.
> 
> The same-ness for either solution can (I think) be fixed by this:
> 
>      put ticks() into T
>      sort lines of myVar by md5digest(T & each)
> 
> or
> 
>      put ticks() into T
>      sort lines of myVar by sha1digest(T & each)
> 
> That should result in random results each time, and is a little faster
> (MD5) or about 1/3 slower (SHA1) than random(999999999) & random(999999999)
> 
> If anyone has thoughts on the collision-or-not-ness of MD5 or SHA1, feel
> free to comment. Otherwise, I hope I'm done now ;-)
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