recode and add prefix to sas variables

Lets's say I have a bunch of variables named the same way and I'd like to recode them and add a prefix to each (the variables are all numeric).

In Stata I would do something like (let's say the variables start with eq)

foreach var of varlist eq* {
    recode var (1/4=1) (else=0), pre(r_)
}

How can I do this in SAS? I'd like to use the %DO macros, but I'm not familiar with them (I want to avoid SQL). I'd appreciate if you could include comments explaining each step!

Solution

SAS syntax for this would be easier if your variables are named using numeric suffix. That is, if you had ten variables with names of eq1, eq2, .... , eq10, then you could just use variable lists to define both sets of variables.

There are a number of ways to translate your recode logic. If we assume you have clean variables then we can just use a boolean expression to generate a 0/1 result. So if 4 and 5 map to 1 and the rest map to 0 you could use x in (4,5) or x > 3 as the boolean expresson.

data want;
  set have;
  array old eq1-eq10 ;
  array new r_eq1-r_eq10 ;
  do i=1 to dim(old);
    new(i) = old(i) in (4,5);
  end;
run;

If you have missing values or other complications you might want to use IF/THEN logic or a SELECT statement or you could define a format you could use to convert the values.

If your list of names is more random then you might need to use some code generation, such as macro code, to generate the new variable names.

Here is one method that use the eq: variable list syntax in SAS that is similar to the syntax of your variable selection before. Use PROC TRANSPOSE on an empty (obs=0) version of your source dataset to get a dataset with the variable names that match your name pattern.

proc transpose data=have(obs=0) out=names;
  var eq: ;
run;

Then generate two macro variables with the list of old and new names.

proc sql noprint ;
  select _name_
       , cats('r_',_name_)
    into :old_list separated by ' '
       , :new_list separated by ' '
  from names
  ;
quit;

You can then use the two macro variables in your ARRAY statements.

  array old &old_list ;
  array new &new_list ;