options ls=80;
data one;
  input x @@;
  retain lastx .;
  if x < lastx then unsort = '*';
  else unsort = ' ';
  thelast = lastx;
  lastx = x;
datalines;
1 3 4 7 8 12 15 18 19 22
;

data two;
  input x @@;
  retain lastx .;
  if x < lastx then unsort = '*';
  else unsort = ' ';
  thelast = lastx;
  lastx = x;
datalines;
1 3 4 7 8 6 15 18 12 22
;

data three;
  input x @@;
*  retain lastx .;
  if x < lastx then unsort = '*';
  else unsort = ' ';
  thelast = lastx;
  lastx = x;
datalines;
1 3 4 7 8 6 15 18 12 22
;

title 'Observations in Order';
proc print data=one;
run;
title 'Two Obs Out of Order';
proc print data=two;
run;
title 'No retain statement';
proc print data=three;
run;