Porter, Allen H ([log in to unmask]) wrote:
: I have a very large ASCII file (270 bytes per record with approx. 1,000,000
: records) that needs to be randomized.  The current program we are using
: takes a couple of hours to run.  Does anyone have a faster method?

I don't know if it would be faster, but here is one way to produce
a random permutation.  Suppose you have t records, numbered 1
through t.

1.  Set j = t.
2.  Generate a random number k in the range 1 through j.
3.  Exchange record k and record j.
4.  Subtract 1 from j.  If j > 1 go to step 2.

This is based on Algorithm P (Shuffling) in 3.4.2, Random Sampling
and Shuffling, in Knuth, The Art of Computer Programming, Volume 2,
Seminumerical Algorithms.

Walter Murray