st: -encode- with predetermined sorting

["Impavido, Gregorio" <GImpavido@imf.org>]

Dear All,

I have the following dataset:

. list
 
      +--------+
      | a    b |
      |--------|
   1. | 10   a |
   2. | 40   b |
   3. | 30   c |
   4. | 20   d |
      +--------+

If I encode b and generate c, I get:

. list *, nolabel
 
      +-------------+
      | a    b   c  |
      |-------------|
   1. | 10   a   1  |
   2. | 40   b   2  |
   3. | 30   c   3  |
   4. | 20   d   4  |
      +-------------+

Now, I want to have a different sort order for c, say as a function of a:

. list *, nolabel
 
      +-------------+
      | a    b   c  |
      |-------------|
   1. | 10   a   1  |
   2. | 40   b   4  |
   3. | 30   c   3  |
   4. | 20   d   2  |
      +-------------+

Is there a more rapid way than the following to obtain what I want?
 
sort a
gen c = _n
forvalues i=1/4 {
	label define lblname `i' "`: di b[`i']'", add
	}
label values c lblname



*
*   For searches and help try:
*   http://www.stata.com/help.cgi?search
*   http://www.stata.com/support/statalist/faq
*   http://www.ats.ucla.edu/stat/stata/