Macro to create new variables with latest values

[Reeza]

How much over are you? Changing the prefix from LAST_ to something shorter may be a quick solution, eg, P_ for prior values would give you 3 more characters to work with. If you're over by a lot then you need to consider renaming.

[ANKH1]

We were not over by much. Using P_ solved it! Thanks again.

[Astounding]

For most of this, macros are not really needed.  This is a program that automatically adapts to the variables you have, except for determining names for the new variables.  That part you have to add yourself.

data want;
   do until (last.id);
      update have (obs=0) have;
      by id;
   end;
   *** The next 3 lines are being hard coded.  If you are clever, it can be automated;
   late_bp = bp;
   late_weight = weight;
   late_bc = bc;
   do until (last.id);
      set have;
      by id;
      output;
      call missing (of late_:);
   end;
run;

The code is untested, so post again if something isn't working for you.

[Quentin]

I like @Astounding's  approach (and wish I could write code like that without testing it : ).

As mentioned, the block of code to create the late_ variables could be automated with a macro.  Since the variable names you want to LOCF will differ, it's helpful if you have a utility macro that will give you a list of the variables in a dataset, something like:

%macro VarList(data) ;
  %local rc varnames ;
  %let rc = %sysfunc(dosubl(%nrstr(
    proc contents data=&data
      out=__VarList(keep=name) noprint ;
    run ;
    proc sql noprint ;
      select name into :varlist separated by ' '
      from __VarList ;   
      drop table __VarList ;
    quit ;
  )));

&varlist /*return*/
%mend ;

Then you can use that macro to build a list of the variables that need to be locf'd.  In below macro, instead of generating an assignment statement to create each last_ variable, I used a RENAME option on the UPDATE statement.  

%macro locf(data=
           ,out=
           ,by=id
           ,nolocf=form_number
           ) ;

  %local
    varlist    /*list of variables in data that will be locf*/
    renamelist /*list of renames to add last_ prefix */
    i
    vari
  ;

  %*build rename list ;
  %let varlist=%varlist(&data(drop=&by &nolocf)) ;

  %do i=1 %to %sysfunc(countw(&varlist,%str( ))) ;
    %let vari=%scan(&varlist,&i,%str( )) ;
    %let renamelist=&renamelist &vari=last_&vari  ;
  %end ;
  
  %*put &=varlist &=renamelist ;

  data &out;
     do until (last.%sysfunc(scan(&by,-1,%str( ))));
        update &data (rename=(&renamelist) obs=0) &data(rename=(&renamelist) );
        by &by;
     end;

     do until (last.%sysfunc(scan(&by,-1,%str( ))));
        set &data;
        by &by;
        output; 
        call missing (of last_:);
     end;
  run;
%mend locf ;

Test like:

data have ;
input ID$ bp weight bc form_number;
datalines;
1 120 78 178 1
1 134 80 177 2
1 143 .  176 3
2 111 58 .   1
3 154 55 160 1
3 178 56 144 2
;
run;

%locf(data=have,out=want)

proc print data=want ;
run ;

That said, I agree with @Reeza also.  The structure of the input data is not weird.  It's great that the input data is in a vertical format.  The output structure you want is unusual, where you essentially merge the results of LOCF back onto the data but only for the first record of each ID.

[Tom]

If you want the last non-missing value per variable then treat the whole dataset as a series of transactions by using the UPDATE statement.

data test;
  input ID $ bp weight bc form_number;
datalines;
1 120 78 178 1
1 134 80 177 2
1 143 . 176 3
2 111 58 . 1
3 154 55 160 1
3 178 56 144 2
;

data want;
  update test(obs=0) test;
  by id;
run;

Which would result in:

                                     form_
Obs    ID     bp    weight     bc    number

 1     1     143      80      176       3
 2     2     111      58                1
 3     3     178      56      144       2

If you need to do it for multiple datasets then get the list of datasets into a dataset and use that to generate the code.

data datasets;
   input input :$41. output :$41.;
cards;
work.test work.want
;

filename code temp;
data _null_;
  set datasets;
  file code;
  put 'data ' output ';' / '  update ' input '(obs=0) ' input ';' / '  by id;' / 'run;' ;
run;
%include code / source2;