Inserting rows into a data set

[jacksonan123]

I have a data set which has two time points at 20 and 24 hrs with corresponding Cp values.  However in some cases the 24 hour sample may be missing.  In those cases I would like to insert a 24 hr time sample with time=24 and cp=0.5*lag(cp) which is the current cp value at 20 hrs.  I have written code which does not give an error but it does not work.  I need to know how to edit the code to get it to work?

DATA SAMPLE;
INPUT ID TIME CP;
DATALINES;
1 20 27
1 24 15
2 20 50
2 24 10
3 20 30
4 20 15
;
DATA EXPAND (KEEP= ID TIME CP CP1 CP2 );
SET SAMPLE ;
TIME1=LAG(TIME);
TIME2=TIME;
CP1=CP;
CP2=LAG(CP);
OUTPUT;
DO ID=1 TO 4;
IF TIME2 = . THEN DO ;
TIME2=24;
OUTPUT;
CP1=0.5*CP2;
OUTPUT;
END;
END;
PROC PRINT;
RUN;

[PeterClemmensen · Accepted solution]

One way

DATA SAMPLE;
INPUT ID TIME CP;
DATALINES;
1 20 27
1 24 15
2 20 50
2 24 10
3 20 30
4 20 15
;

data want;
    set sample;
    by id;
    output;
    if first.id & last.id then do;
        TIME=24; CP=CP/2;
        output;
    end;
run;

Result:

id  time CP
1	20	 27
1	24	 15
2	20	 50
2	24	 10
3	20	 30
3	24	 15
4	20	 15
4	24	 7.5

[data_null__]

This?

DATA SAMPLE;
INPUT ID TIME CP;
DATALINES;
1 20 27
1 24 15
2 20 50
2 24 10
3 20 30
4 20 15
;;;;
   run;
data want;
   set sample;
   by id;
   output;
   if last.id and time ne 24 then do;
      time = 24;
      cp = .5 *cp;
      output;
      end;
   run;
proc print;
   run;