Re: st: Data management: code to be able to..

[Phil Schumm <pschumm@uchicago.edu>]

On Jun 3, 2007, at 3:09 PM, S J wrote:
> I have a string identifier variable of the form:
>
> id
> "LOCALITY_NAMED_ABCD 001"
> "LOCALITY_NAMED_F 060"
> "HOUSTON 078"
> "SAN ANTONIO 112"
>
> The variable id thus has both the name of the locality in question  
> (say, HOUSTON), and an identifying code (say, 078).
>
> How can I generate a new variable, idcode, that only captures the  
> numeric component of id, so that, I get, for the above 4 cases, the  
> values below:
>
> idcode
> 1
> 60
> 78
> 112

If you can assume that in all cases the ID code will be preceded by a  
space *and* has no embedded spaces itself (e.g., "CHICAGO 112 09"  
where the ID code is "112 09"), then the following will work:


gen idcode = substr(trim(id),-strpos(reverse(trim(id))," ")+1,.)


Note that this allows for the possibility that (1) the ID code is  
variable in length, and (2) the entire string has trailing spaces.

BTW, this is a situation where it would be nice to have a function  
that returned the nth subexpression from a regular expression match  
variable-wise (as opposed to the function -regexs()-, which, I  
believe, can only handle one observation at a time).  For example, if  
there were such a function (call it -foo()-) and if we could assume  
that the ID code were always an integer, we could write something  
like the following:

gen idcode = foo(id,"^.+[ ]+([0-9]+)[ ]*",1)

where we are setting idcode equal to the first subexpression of the  
match.  Although the first approach based on -substr()- is probably  
adequate in this case, the latter approach is -- for those used to  
working with regular expressions -- much more readable.


-- Phil

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