/*The Data we have is this:*/

DATA Temp;
Input Var200203 Var200204 Var200205 VarLookUp $11.;
DataLines;
1 2 3 Var200203
5 6 7 Var200204
3 6 9 Var200205
;
RUN;

/*We want to end up with VarOut which is the value of the lookup column for that observation:

Var200203 Var200204 Var200205 VarLookUp VarOut
1         2         3         Var200203 1
5         6         7         Var200204 6
3         6         9         Var200205 9
*/

/*The solution:

While the vname function is comparatively expensive, it’s helpful here.
One additional data line added to test with unexpected data.*/

DATA Temp;
Input Var200203 Var200204 Var200205 VarLookUp $11.;
DataLines;
1 2 3 Var200203
5 6 7 Var200204
3 6 9 Var200205
3 6 9 Var200206
;
data done ( drop = _: ); set temp; array vars var2: ; do _i = 1 to dim(vars) until (vname(vars(_i)) = varlookup) ; end; if _i le dim(vars) then varout = vars(_i); run;

proc print data=done;
run;

/*
The SAS System                      09:21 Thursday, July 31, 2003   1

Obs    Var200203    Var200204    Var200205    VarLookUp    varout

1         1            2            3        Var200203       1
2         5            6            7        Var200204       6
3         3            6            9        Var200205       9
4         3            6            9        Var200206       .
*/

http://jaredprins.squarespace.com/blog/2008/3/31/setting-variable-value-based-on-value-of-another-variable.html

Setting variable value based on value of another variable.

SAS