Changing a date variable in three rows

[EinarRoed]

I have a data set with two date variables, FROM_DTTM and TO_DTTM. There's four rows. For the first three rows, I need to make TO_DTTM be equal to FROM_DTTM plus one second. The fourth row should remain unchanged.

Can someone please suggest what kind of code to use for this? I know I can use FIRST. and LAST. to identify the first and last rows, but I don't know about the second and third. Perhaps a while-loop with a count would be best? Alas I remain a bit inexperienced about programming. Please be specific if you can.

Thanks for your time.

[Patrick · Accepted solution]

For your very specific case, assuming that you have only 4 rows in the table and assuming that to_dttm and from_dttm contain SAS datetime values:

data ...

set ...

if _n_<=3 then TO_DTTM=FROM_DTTM+1;

...

run;

This looks very much like something related to SCD2. If so then TO_DTTM should actually be 1 second less than FROM_DTTM of the NEXT record (and not within the same record).

Is this about aligning records which got loaded using type 2 loading techniques. Is so let us know and if possible also post your data as the alignment needs then to be done a bit different as shown in the pseudo code I've posted.