macro variable is uninitialized after %let statement in sas

Question

I want to create something in SAS that works like an Excel lookup function. Basically, I set the values for macro variables var1, var2, ... and I want to find their index number according to the ref table. But I get the following messages in the data step.

NOTE: Variable A is uninitialized.
NOTE: Variable B is uninitialized.
NOTE: Variable NULL is uninitialized.

When I print the variables &num1,&num2, I get nothing. Here is my code.

data ref;
    input index varname $;
    datalines;
0 NULL
1 A
2 B
3 C
;
run;

%let var1=A;
%let var2=B;
%let var3=NULL;

data temp;
    set ref;
    if varname=&var1 then call symput('num1',trim(left(index)));
    if varname=&var2 then call symput('num2',trim(left(index)));
    if varname=&var3 then call symput('num3',trim(left(index)));
run;

%put &num1;
%put &num2;
%put &num3;

I can get the correct values for &num1,&num2,.. if I type varname='A' in the if-then statement. And if I subsequently change the statement back to varname=&var1, I can still get the required output. But why is it so? I don't want to input the actual string value and then change it back to macro variable to get the result everytime.

Answer 1

Solution to immediate problem

You need to wrap your macro variables in double quotes if you want SAS to treat them as string constants. Otherwise, it will treat them the same way as any other random bits of text it finds in your data step.

Alternatively, you could re-define the macro vars to include the quotes.

As a further option, you could use the symget or resolve functions, but these are not usually needed unless you want to create a macro variable and use it again within the same data step. If you use them as a replacement for double quotes they tend to use a lot more CPU as they will evaluate the macro vars once per row by default - normally, macro vars are evaluated just once, at compile time, before your code executes.

A better approach?

For the sort of lookup you're doing, you actually don't need to use a dataset at all - you can instead define a custom format, which gives you much more flexibility in how you can use it. E.g. this creates a format called lookup:

proc format;
  value lookup
  1 = 'A'
  2 = 'B'
  3 = 'C'
  other = '#N/A' /*Since this is what vlookup would do :) */
  ;
run; 

Then you can use the format like so:

%let testvar = 1;
%let testvar_lookup = %sysfunc(putn(&testvar, lookup.));

Or in a data step:

data _null_;
  var1 = 1;
  format var1 lookup.;
  put var1=;
run;