Read previous and next observations

Question

I have a dataset like this(sp is an indicator):

datetime        sp
ddmmyy:10:30:00 N
ddmmyy:10:31:00 N
ddmmyy:10:32:00 Y
ddmmyy:10:33:00 N
ddmmyy:10:34:00 N
         


        

Answer 1

Try using the point option in set statement in data step. Like this:

data extract;
set surprise_6_step2 nobs=nobs;
if sp = 'Y' then do;
  current = _N_;
  prev = current - 1;
  next = current + 1;

  if prev > 0 then do;
    set x point = prev;
    output;
  end;

  set x point = current;
  output;

  if next <= nobs then do;
    set x point = next;
    output;
  end;
end;

run;

There is an implicite loop through dataset when you use it in set statement. _N_ is an automatic variable that contains information about what observation is implicite loop on (starts from 1). When you find your value, you store the value of _N_ into variable current so you know on which row you have found it. nobs is total number of observations in a dataset.

Checking if prev is greater then 0 and if next is less then nobs avoids an error if your row is first in a dataset (then there is no previous row) and if your row is last in a dataset (then there is no next row).

Answer 2

/* generate test data */
data test;
    do dt = 1 to 100;
        sp = ifc( rand("uniform") > 0.75, "Y", "N" );
        output;
    end;
run;

proc sql;
    create table test2 as
        select  *,
            monotonic() as _n
        from  test
    ;
    create table test3 ( drop= _n ) as
        select  a.*
        from    test2 as a
        full join   test2 as b
            on  a._n = b._n + 1
        full join   test2 as c
            on a._n = c._n - 1
        where   a.sp = "Y"
            or b.sp = "Y"
            or c.sp = "Y"
    ;
quit;