topic reverse of lag function? in SAS Procedures

reverse of lag function?

jaxonmills — Mon, 23 Jan 2012 08:27:53 GMT

How can I go from this:

a1 b1 c1 z1

a2 b2 c2 z2

a3 b3 c3 z3

to this:

a1 b1 c1 z2

a2 b2 c2 z3

a3 b3 c3 z4

without lagging the a, b, and c variables? Is there a way to pull back the z variable?

The reason I'd like to avoid this is because I've got many variables of the a, b, and c type that I don't want to mess with / rename, and only one like the z variable that I'd like to move back to the preceding observation.

Thanks.

reverse of lag function?

art297 — Mon, 23 Jan 2012 12:11:53 GMT

One possibility is the look ahead, look back method as described at:

It is based on the look ahead look back method that is described at:http://www.sascommunity.org/wiki/Look-Ahead_and_Look-Back

However, you would only need to apply the look ahead part, as you appear to want to apply the next z value to each current record.

reverse of lag function?

Alfredo — Mon, 23 Jan 2012 13:15:54 GMT

Try this:

data b;

merge a(keep=a b c) a(keep=z firstobs=2);

run;

reverse of lag function?

art297 — Mon, 23 Jan 2012 13:23:08 GMT

Alfredo, That is basically the look ahead method. It is easier, though, to simply drop the look ahead variable from the first file, rather than explicitly keep all of the others. And if you are going to use merge rather than 2 set statements, you have to insure you have the correct setting for the mergenoby option.

Re: reverse of lag function?

data_null__ — Mon, 23 Jan 2012 13:32:47 GMT

proc expand data=sashelp.class out=lead;
   convert weight=leadWeight  / method=none transformout=(lead 1);
   run;
proc print;
   run;

Re: reverse of lag function?

LarryWorley — Mon, 23 Jan 2012 14:16:38 GMT

But you need ETS for proc expand:-(

Re: reverse of lag function?

data_null__ — Mon, 23 Jan 2012 15:01:03 GMT

Yes they should move it to BASE. Jim?

Re: reverse of lag function?

art297 — Mon, 23 Jan 2012 15:03:55 GMT

And, if he is listening, AF should be moved there as well.

Re: reverse of lag function?

jaxonmills — Mon, 23 Jan 2012 23:33:39 GMT

Thanks for the help guys. I'll give these a try and get back to you.

Re: reverse of lag function?

jaxonmills — Tue, 24 Jan 2012 01:18:11 GMT

Thanks, got it!!