Flag consecutive and non consecutive dates

[NewUsrStat]

Guys,
I need to do the following but I don't know how.
I need to distinguish the first case from the second:

case1:

     ID          Start                  End  

   0001           -               18DEC2019
   0001    19DEC2019             -

case2:

   ID           Start                   End  

   0001           -               18DEC2019
   0001    11JAN2020             -

Meaning, is there a way to flag if the end is continuous with the start from the case in which there is a gap from the previous end and the next start? Continuity in terms of years is sufficient.

Thank you in advance

[mkeintz · Accepted solution]

If the data are sorted by ID/start, then:

data want (drop=next_:);
  set have (keep=id);
  by id;
  merge have
        have (firstobs=2 keep=start rename=(start=next_start);

  if first.id=1 or start-1 ^=lag(end) then backward_consecutive='N';
  else backwards_consecutive='Y';

  if last.id=1 or end+1 ^= next_start then forward_consecutive='N';
  else forward_consecutive='Y';
run;

This uses a self-merge with offset approach  (i.e. the firstobs=2 in one of the MERGE argument.  It also uses SET plus BY statements to generate the first.id and last.id dummies.

[NewUsrStat]

Thank you very much! It works perfectly!