topic defining lagged values in SAS Programming

defining lagged values

issac — Mon, 20 Aug 2012 22:16:57 GMT

Hi everyone;

I have two columns in the data, named seq and los and want to define new variables named laglos, which get the same value when seq=1 and when seq>1, I want it to get the value los for previous seq value. For example

seq	los	laglos
1	14	14
1	3	3
2	5	3
3	7	5
1	9	9
2	13	9
1	3	3
1	5	5
2	6	5
3	8	6
4	9	8
5	11	9
6	4	11

I try this but it does not work:

data new;

set old;

if seq=1 then laglos=los;

output;

else laglos=lag1(los);

output;

run;

Thanks!

Issac

Re: defining lagged values

data_null__ — Mon, 20 Aug 2012 22:34:54 GMT

laglos=ifn(seq eq 1,los,lag(los));

Re: defining lagged values

Haikuo — Mon, 20 Aug 2012 22:37:49 GMT

Well, another victim of twisted lag(). Lag() is the one function whose function can't be correctly deduced from its name. Here is a way, of course you can also use retain:

data old;

input seq los laglos;

cards;

1 14 14

1 3 3

2 5 3

3 7 5

1 9 9

2 13 9

1 3 3

1 5 5

2 6 5

3 8 6

4 9 8

5 11 9

6 4 11

;

data new;

set old;

laglos=ifn(seq=1,los,lag(los));

run;

proc print;run;

Your original code has two unnecessary output statements, and one of them was wrongly inserted between if and else. If you need to do more than one thing, you need to use do-loop.

Haikuo

Re: defining lagged values

Haikuo — Mon, 20 Aug 2012 22:41:53 GMT

Glad to know you are here, DN. I have always wanted to ask, why lag() changes behavior when inside ifn()?

Thanks,

Haikuo

Re: defining lagged values

art297 — Mon, 20 Aug 2012 22:53:48 GMT

Haikuo: take a look at: http://www.sascommunity.org/wiki/Conditional_Use_of_LAG

Re: defining lagged values

issac — Mon, 20 Aug 2012 23:07:05 GMT

Thanks so much for all of you guys!

Re: defining lagged values

Haikuo — Mon, 20 Aug 2012 23:34:08 GMT

Thanks, Art. Now I understand that inside ifn() or ifc(), the lag() is always called.

Haikuo

Re: defining lagged values

Astounding — Tue, 21 Aug 2012 02:49:07 GMT

Good to know. If for some reason you don't have IFN, you can always make sure LAG gets used every time:

laglos = lag(los);

if seq=1 than laglos = seq;