Use LAG to get previous value. When it is the first record for the admit date then overwrite that with the admit date. data have; informat admdate testdate mmddyy10.; format admdate testdate mmddyy10. ; input pid $ admdate : testdate : group $ @@; cards; 1 1/1/2011 1/3/2011 A 1 1/1/2011 1/9/2011 B 1 3/4/2011 4/2/2011 B 1 3/4/2011 4/8/2011 B 2 6/1/2010 6/4/2011 C 2 6/5/2010 7/4/2011 C 3 7/1/2011 7/9/2011 D run; proc sort; by pid admdate testdate ; run; data want ;   set have ;   by pid admdate testdate ;   prevdate = lag(testdate) ;   format prevdate mmddyy10.;   if first.admdate then prevdate=admdate;   diff = testdate - prevdate ;   put pid admdate prevdate testdate diff group ; run; 1 01/01/2011 01/01/2011 01/03/2011 2 A 1 01/01/2011 01/03/2011 01/09/2011 6 B 1 03/04/2011 03/04/2011 04/02/2011 29 B 1 03/04/2011 04/02/2011 04/08/2011 6 B 2 06/01/2010 06/01/2010 06/04/2011 368 C 2 06/05/2010 06/05/2010 07/04/2011 394 C 3 07/01/2011 07/01/2011 07/09/2011 8 D ... View more

Use %sysevalf( &sysver > 9.2) to test if you are running a version newer than 9.2. I agree that the NOTE is inappropriate.  It does seem strange that even when you ask for keyword format it does not return it, but changing the output now might break old code. Also I would like them to fix the strings returned for values that require quotes when assigning the values. For example if you try this code you will get error messages: options missing=" "; %let sopt=%sysfunc(getoption(missing,keyword)); options &sopt; What I have done is something like: %let sopt=formchar="%qsysfunc(getoption(missing))"; Here is the list of options that I indentified a couple of years ago that require that treatment. missing invaliddata formchar formdlim topmargin leftmargin rightmargin bottommargin xprintnm printerpath ... View more

It helps to look at some example data. data test;   do a=1 to 3; do b=1 to 3; do c=1 to 3; output; end; end; end; run; data _null_;    set test;    by a b ;    put (a first.a last.a b first.b last.b c) (=); run; a=1 FIRST.a=1 LAST.a=0 b=1 FIRST.b=1 LAST.b=0 c=1 a=1 FIRST.a=0 LAST.a=0 b=1 FIRST.b=0 LAST.b=0 c=2 a=1 FIRST.a=0 LAST.a=0 b=1 FIRST.b=0 LAST.b=1 c=3 a=1 FIRST.a=0 LAST.a=0 b=2 FIRST.b=1 LAST.b=0 c=1 a=1 FIRST.a=0 LAST.a=0 b=2 FIRST.b=0 LAST.b=0 c=2 a=1 FIRST.a=0 LAST.a=0 b=2 FIRST.b=0 LAST.b=1 c=3 a=1 FIRST.a=0 LAST.a=0 b=3 FIRST.b=1 LAST.b=0 c=1 a=1 FIRST.a=0 LAST.a=0 b=3 FIRST.b=0 LAST.b=0 c=2 a=1 FIRST.a=0 LAST.a=1 b=3 FIRST.b=0 LAST.b=1 c=3 a=2 FIRST.a=1 LAST.a=0 b=1 FIRST.b=1 LAST.b=0 c=1 a=2 FIRST.a=0 LAST.a=0 b=1 FIRST.b=0 LAST.b=0 c=2 a=2 FIRST.a=0 LAST.a=0 b=1 FIRST.b=0 LAST.b=1 c=3 a=2 FIRST.a=0 LAST.a=0 b=2 FIRST.b=1 LAST.b=0 c=1 a=2 FIRST.a=0 LAST.a=0 b=2 FIRST.b=0 LAST.b=0 c=2 a=2 FIRST.a=0 LAST.a=0 b=2 FIRST.b=0 LAST.b=1 c=3 a=2 FIRST.a=0 LAST.a=0 b=3 FIRST.b=1 LAST.b=0 c=1 a=2 FIRST.a=0 LAST.a=0 b=3 FIRST.b=0 LAST.b=0 c=2 a=2 FIRST.a=0 LAST.a=1 b=3 FIRST.b=0 LAST.b=1 c=3 a=3 FIRST.a=1 LAST.a=0 b=1 FIRST.b=1 LAST.b=0 c=1 a=3 FIRST.a=0 LAST.a=0 b=1 FIRST.b=0 LAST.b=0 c=2 a=3 FIRST.a=0 LAST.a=0 b=1 FIRST.b=0 LAST.b=1 c=3 a=3 FIRST.a=0 LAST.a=0 b=2 FIRST.b=1 LAST.b=0 c=1 a=3 FIRST.a=0 LAST.a=0 b=2 FIRST.b=0 LAST.b=0 c=2 a=3 FIRST.a=0 LAST.a=0 b=2 FIRST.b=0 LAST.b=1 c=3 a=3 FIRST.a=0 LAST.a=0 b=3 FIRST.b=1 LAST.b=0 c=1 a=3 FIRST.a=0 LAST.a=0 b=3 FIRST.b=0 LAST.b=0 c=2 a=3 FIRST.a=0 LAST.a=1 b=3 FIRST.b=0 LAST.b=1 c=3 ... View more

You want to reset the counter when FIRST.DATE is true.  You do not care about the status of the FIRST. variables for earlier variables in the BY statement. ... View more

As long as you are using SAS verison 9 you should be able to use the COUNTW function. %let n=%sysfunc(countw(&macrolist)); Otherwise you can loop and increment your own counter.  You can either test for empty using something like: %if (&var = ) %then .... Or test for zero length %if %length(&var)=0 %then ... They test slightly different things, but for this problem they are equivalent as you are using blanks for your delimiter. Here is one way to count. Remember to subtract one because it stops on an empty word. %let n=1 ; %do %while(%scan(&macrolist),&n) ne ) ;     %let n=%eval(&n + 1); %end; %let n=%eval(&n -1 ); ... View more

The %str( ) is useful to prevent the macro processor from ignoring the space. When you use single quotes or double quotes around characters they actually become part of the string. This means that %scan(&myvar,&i,%str( )) means something different than %scan(&myvar,&i,' '). The first only uses blanks as the delimiter when scanning.  The second one will use either blanks or single quote characters. ... View more