SAS array DO loop calculation within data step

Question

I have the following data set:

data have;
    input x10 x22 x13 x64;
cards;
20 10 30 1
;
run;

I want to create four new columns called log_x10, log_x22, log_x13, log_x64 which are the logs of the original columns. I know this is probably a fairly straightforward array, loop process, but I'm fairly new to arrays and can't quite get the syntax. Here is what I have:

data want;
    set have;
    array var[*] x: ;
    do j=1 to dim(var);
        logx[j]=log(var[j]);
    end;
run;

It won't always be four variables, sometimes less or more. I have the id numbers pulled into a macrolist id=(10,22,13,64) so can try to use something like that to name.

Ideas? Thanks.

Answer 1

I think you'll need to establish the length of your array at in order to declare your result array. Fortunately you can load it into a macro variable with with short datastep.

data have;
    input x10 x22 x13 x64;
cards;
20 10 30 1
;
run;

data _null_;
    set have (obs=1);
    array vars[*] x: ;
    call symput('array_length',cats(dim(vars)));
run;

data want;
    length logx1-logx&array_length. 8;
    set have;
    array vars[*] x: ;
    array logvars[*] logx1-logx&array_length.;
    do j=1 to dim(vars);
        logvars[j]=log(vars[j]);
    end;
run;