topic Lag function in SAS Procedures

Lag function

Matt_Lin — Thu, 25 Jul 2013 13:56:03 GMT

Hi All,

I just realized that, if there is some condition before using LAG the function, then LAG will take the "previous one" from those that satisfy the condition ?

For example,

n A Name C

1 0 Abbie

2 1 Bob

3 . Charlie

4 0 David

5 1 Eddie

6 . Frank

If A = . then C = lag(B);

for record # 6, C will have Charlie, not Eddie.

How do I get Eddie ??

Many Thanks for quick response, working in the office now...

Re: Lag function

Haikuo — Thu, 25 Jul 2013 14:02:38 GMT

When using lag() /dif() conditionally, you need to be aware of what is happening, in your case, you need using it unconditionally:

c=ifc(missing(a), lag(b), c);

In this case, lag() will be processed for every row of record, another option is to create a new variable to address the lag() scenario, then drop it.

Please read SAS help Docs on lag() for deeper understanding.

Haikuo

Re: Lag function

Matt_Lin — Thu, 25 Jul 2013 14:55:12 GMT

Thanks! I understand.

But there is more to the question when more than 1 row is missing consecutively: (and number of missing rows is indefinite)

n A Name C (intended answer) C(currently achieved using either method)

1 1 Abbie Abbie Abbie

2 . Bob Abbie Abbie

3 . Charlie Abbie .

4 1 David David David

5 . Eddie David David

6 . Frank David .

7 . George David .

If I kept running SAS code your suggested manually, it will work out "eventually" (3 David -> 4 David -> etc...), but that won't be a solution.

Many many thanks !

Re: Lag function

Haikuo — Thu, 25 Jul 2013 15:11:40 GMT

Well, in that case, you would need something a little different:

data havE;

input n A Name $;

cards;

1 1 Abbie

2 . Bob

3 . Charlie

4 1 David

5 . Eddie

6 . Frank

7 . George

;

data want;

set have;

length c $ 8;

retain c;

if not missing(a) then c=name;

run;

Haikuo

Re: Lag function

Matt_Lin — Thu, 25 Jul 2013 15:21:11 GMT

YES! That is what I want!

man, you are a genius !