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Re: st: Unique identifier from a string name


From   brendan.halpin@ul.ie (Brendan Halpin)
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: Unique identifier from a string name
Date   Thu, 24 Nov 2011 11:48:21 +0000

On Thu, Nov 24 2011, Barry Quinn wrote:

> I would like to create a uniquely identified numerical code from a
> string variable by ideally converting each letter of the string into a
> number (but any other solutions that could create a unique identifier
> from a string are welcomed).
> Is there some way of reversing the function char() to do this ?

-encode- will do it, as long as your dataset is fixed (i.e. there will
be a fixed one-to-one relationship between string and number that
depends on what data is there when the command is issued).

If you want a deterministic relationship between any possible string and
its integer, you'll need another solution. For short strings something
conceptually similar to:

char(substr(string,1,1)) + 256*(
  char(substr(string,2,1)) + 256*(
    char(substr(string,3,1)) + 256*(
      char(substr(string,4,1)) + 256*(
        char(substr(string,5,1)) + 256*(
...)))))

will work, but will soon generate numbers you can't store (and assumes
char is a byte).

I've often thought that Stata should have an MD5 hash function for
situations like this. 

Brendan
-- 
Brendan Halpin,   Department of Sociology,   University of Limerick,   Ireland
Tel: w +353-61-213147  f +353-61-202569  h +353-61-338562;  Room F1-009 x 3147
mailto:brendan.halpin@ul.ie    ULSociology on Facebook: http://on.fb.me/fjIK9t
http://teaching.sociology.ul.ie/bhalpin/wordpress         twitter:@ULSociology
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