General SAS Programming

[factorhedge]

Hi

I have a longitudinal dataset with many firms each month , 9 years so I have (12*9) months for each firm an example of my dataset is mentioned below.

ID	Monthend(MM/YYYY)	Returns(%)	Level (Diff in Returns)
1212	082003	2.5
1212	092003	2.8	2.8-2.5
1212	102003	2.0
1212	012004	3.1
1213	052005	4.0
1213	062005	5.0
1214	022008	2.3
1214	032008	1.2

I would like to compute the variable 'Level" which is the difference in returns from T+1 and T . For example the Level for the ID 1212 in 092003 = Returns in 092003 - 082003 (2.8% - 2.5%). This should be for each ID , that is when the ID changes the first observation in Level variable should be '0' and from 2nd observation the difference is computed.

I was wondering whether First.ID and Last.ID method works for this. Could someone send me a sample code.

[Reeza · Accepted solution]

There's also the DIF() function

data want;

set have;

by id;

level=dif(returns);

if first.id then level=0;

run;

[naveen_srini]

data want;

set have;

by id;

k=lag(returns);

if not first.id then level=returns-k;

drop k;

run;

[factorhedge]

Thank you , both the codes works fine for me

[Reeza · Accepted solution]

There's also the DIF() function

data want;

set have;

by id;

level=dif(returns);

if first.id then level=0;

run;