Set value of a variable determined at run-time (inverse of VVALUEX function)

[cr2]

The VVALUEX function allows fetching the value of a variable determined at run-time, by passing as argument another variable, for each observation. 

For example, the following statement in a datstep:

NEW_FIELD = vvaluex(DYN_FIELD);

Would produce the following result:

DYN_FIELD	A	B	C	NEW_FIELD
A	1	2	3	1
A	5	6	7	5
B	9	10	11	10
C	13	14	15	15

I would like to perform the inverse: set a value of a variable determined at run-time, ideally, a function such as this, callable from within a datastep:

call SETVALUEX(DYN_FIELD, SOURCE_FIELD);

DYN_FIELD	A	B	C	SOURCE_FIELD
A	1	.	.	1
A	2	.	.	2
B	.	3	.	3
C	.	.	4	4

[Tom · Accepted solution]

Why not just use an array?

%let varlist=A B C ;
%let n=%sysfunc(countw(&varlist));
%let namelist="%sysfunc(tranwrd(&varlist,%str( )," "))";
data want ;
  set have ;
  array vars &varlist ;
  array varnames (&n) $32 _temporary_ (&namelist);
  vars(whichc(dyn_field,of varnames(*))=source_field;
run;

You could generate the needed macro variables from the data.

proc sql noprint;
select distinct dyn_field,quote(trim(dyn_field))
  into :varlist separated by ' '
     , :varnames separated by ' '
  from have
;
%let n=&sqlobs;
quit;

[cr2]

Not as clean as one would want, but it works perfectly.

Thanks!

[34reqrwe]

I had never came across these functions before. they are really interesting thanks. 

I managed to get the desired result by adding the VVALUE function :

data HAVE;
	dyn_field='A';
	A = 1;
	B=.;
	C=.;
	OUTPUT;
	dyn_field='A';
	A = 2;
	B=.;
	C=.;
	OUTPUT;
	dyn_field='B';
	A = .;
	B=3;
	C=.;
	OUTPUT;
	dyn_field='C';
	A = .;
	B=.;
	C=4;
	OUTPUT;
RUN;

DATA WANT;
	SET HAVE;
	SOURCE_FIELD=STRIP(VVALUEX(STRIP(VVALUE(DYN_FIELD))));
RUN;

[Ksharp]

SAS/IML has such function, check CALL SETVAL() .