No comments on the "collision-or-not-ness", but some concerns about
performance.
The performance of "random() & random()" is conveniently
data-independent, but that for md5digest() is not. With nice short
lines, it is indeed faster than the random&random version, but as the
line size increases, so does the time taken by all of the digest
methods. I didn't test it thoroughly, but the swap-over point is fairly
low - somewhere around 500 chars per line.
-- Alex.
On 04/06/2013 18:51, 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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