* clog.sas Daniel Brockman 070729 Calc natural log for specified variables ;

* tested 070729;

%macro clog(vlist) ;

/* 
* vlist  = names of vars of interest, separated by spaces
*
* Invoke %clog within a data step.
*
* We calculate the natural logarithm on each date for each 
* var listed in vlist. We replace the value of the variable
* with the log of the value.
*
* nb. This seems like a lot of macrofluff just to calculate a logarithm.
* Might this be done in a more straightforward way in the calling program?
* We do it in the macro because (1) we want to calculate the logs of 
* a general and unpredictable list of variables, (2) we cant do a macro 
* loop through the variables of interest in open code, (3) doing an 
* equivalent calculation with data step arrays seems more complex (tho
* I didn't try it), because we don't know the order of the relevant 
* vars in the dataset.
*/

  %let ii=0;
  %do %until (%scan(&vlist,%eval(&ii+1)) eq  ) ;  * loop the variable list ;
    %let ii=%eval(&ii+1);
    %let varii=%scan(&vlist,&ii);
    &varii=log(&varii);      * replace value with natural log of value ;
    %end ;

%mend clog ;