data aa;
  input a;
  cards;
1
2
2
7
1
23
2
1
10
23
12
11
;
run;

1111111111111111111111111111111111111
data bb;
  set aa;
  a1=lag2(a);
  a2=lag(a);
  a3=a;
  if a2=10 then output;
  drop a;
run;
proc print;run;


2222222222222222222222222222222222222
proc transpose data=aa out=cc;
run;
data dd;
  set cc;
  array ar[12] col1-col12;
  do i=1 to 12;
    if ar(i)=10 then do;
   x1=ar(i-1);
   x2=ar(i);
   x3=ar(i+1);
end;
  end;
  keep x1-x3;
run;
proc print;run;

两种方法，扩展性不强

你的意思是把观测值为10以及他的前后各一个观测都保留下来？试试这个程序：
data aa;
  input a @@;
  cards;
10 2 3 4 5 6 7 8 90 10 10 12 10
;
run;
data bb;
set aa;
if a=10 then do;
na=_n_-1;output;
na=_n_ ;output;
na=_n_ +1;output;
end;
run;
proc sql;
create table b1 as select distinct na from bb;
quit;
data want(keep=a);
set b1;
do i=na;
set aa point=i;
if _error_=0 then output;
end;
run;
proc print;run;