non-consecutive/ consecutive dates?

[RAVI2000]

How to print non-consecutive / consecutive dates from given set of dates?

Data x;
Input patid date mmddyy10.;
Datalines;
1001 02/01/10
1001 02/02/10
1001 02/03/10
1002 02/01/10
1002 02/03/10
1002 02/05/10
;
Run;

Can anyone explain the detailed logic step by step?

[PeterClemmensen]

What is your desired resultat here?

[Kurt_Bremser]

data want;
set x;
by patid;
flag = (not first.patid and date ne lag(date) + 1);
run;

[mkeintz]

This might be a good situation to use the DIF function, where  dif(x) is equivalent to x - lag(x):

data want;
  set have;
  by patid;
  if first.patid=0 and dif(date)=1 then consecutive='Y';
  else consecutive='N';
run;