making dummy variables for existence of row information in two- and three in a row

[sas_user_k]

data example;
	input firmname $ year revenue;
	cards;
APPLE 1991 102
APPLE 2004 232
APPLE 2005 322
APPLE 2006 231
APPLE 2007 234
APPLE 2009 421
APPLE 2010 231
APPLE 2011 442
APPLE 2012 422
APPLE 2013 212
MSMFT 2000 323
MSMFT 2001 231
MSMFT 2004 232
MSMFT 2005 152
MSMFT 2006 345
MSMFT 2007 232
MSMFT 2009 231
MSMFT 2010 341
MSMFT 2011 325
run;

Hi. I am trying to set two dummy variables for the example shown above, depending on whethter, for each firm ('APPLE' and 'MSMFT'), the 'revenue' information exist 1) in two-years in a row and 2) in three-years in a row, and the output should look like below. Thank you in advance!

firmname   year   revenue   two   three

APPLE	1991	102	0	0
APPLE	2004	232	0	0
APPLE	2005	322	1	0
APPLE	2006	231	1	1
APPLE	2007	234	1	1
APPLE	2009	421	0	0
APPLE	2010	231	1	0
APPLE	2011	442	1	1
APPLE	2012	422	1	1
APPLE	2013	212	1	1
MSMFT	2000	323	0	0
MSMFT	2001	231	1	0
MSMFT	2004	232	0	0
MSMFT	2005	152	1	0
MSMFT	2006	345	1	1
MSMFT	2007	232	1	1
MSMFT	2009	231	0	0
MSMFT	2010	341	1	0
MSMFT	2011	325	1	1

[Astounding · Accepted solution]

This looks like it should work.  I can't test it right now, but give it a shot and see what you get.

data want;

set have;

by firmname;

retain consecutive_count;

years_passed = dif(year);

if first.firmname then consecutive_count=1;

else do;

   if years_passed=1 then consecutive_count + 1;

   else consecutive_count=1;

end;

if consecutive_count >= 2 then two=1;

else two=0;

if consecutive_count >= 3 then three=1;

else three=0;

run;

[sas_user_k]

Thank you! The code your provided works well!