Re: st: RE: looping over bys groups?

[Jeph Herrin <junk@spandrel.net>]

Thanks Nick, David, these were the kind of tips I was looking for. Don't
know why it didn't occur to me to reverse the sort order on date,  which
solves a number of problems, and confess I have only ever made cursory use of
postfiles, so didn't consider the usefulness here. I'll give it another go
and see what emerges.

cheers,
Jeph


David Elliott wrote:
> I've done something very similar in the past only it was in a database
> program.  I sorted the data on patient in ascending order, but within
> patient in descending date order so one worked toward the past as Nick
> has suggested.  What I did, however, was to write my results to a new
> file as I scanned the old one.  Stata would allow you to do this with
> postfile where you would duplicate the information of the variables in
> your original data and also add the derived variables  for switch,
> interval, etc., posted to the postfile.
>
> In greater detail: Original file (A), postfile (B)
>
> [commands to create a postfile]
> forvalues i=1/`c(N)' {
>  [commands to read in A[`i'] variables]
>  local this_scrssn scrssn[`i']  //initialize scrssn
>  local j = `i'
>  while scrssn[`j']== `this_scrssn'  & `j' <= `c(N)'  { // while same 
> individual
>    local ++j
>    [commands to read in A[`j'] variables]
>    [logic to compare `i'th prescription to `j'th prescription and
> decide if add or switch]
>    [post to B]
>    continue //break out of while once we are sure about the index 
> prescription
>  }
> }
>
> and so on.  I have left it to you to fill in the [black boxes] (I'm
> put in mind of this famous cartoon:
> http://www.people.virginia.edu/~del6n/miracle.jpg ).  I'd be
> interested to see how this comes out.
>
> DCE
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