topic Flagging an observation that is different from the previous one in SAS Programming

Flagging an observation that is different from the previous one

Dregerator — Mon, 25 Nov 2019 06:03:45 GMT

Lets say in this dataset I have repeated measures for one subject. However, I want to flag if the next observation is different from the previous one...for example the dataset looks like this

Subject Event

1 A

1 B

1 A

1 C

1 A

1 B

1 C

Now I want to flag if the next event is different from the prior one and my output should mark these values as a flag

Subject Event Flag

1 A Y

1 B Y

1 A Y

1 A

1 C Y

1 A Y

1 B Y

1 B

1 C Y

Is there a way to do this?

Re: Flagging an observation that is different from the previous one

PeterClemmensen — Mon, 25 Nov 2019 06:36:26 GMT

Looking at the wanted result, it seems that what you want to do is set flag to 'Y' when the previous event is different from the current?

data have;
input Subject Event $;
datalines;
1 A
1 B
1 A
1 A
1 C
1 A
1 B
1 B
1 C
;

data want;
   set have;
   if event ne lag1(event) then flag='Y';
run;

Result:

Subject Event flag 
1       A     Y 
1       B     Y 
1       A     Y 
1       A       
1       C     Y 
1       A     Y 
1       B     Y 
1       B       
1       C     Y

Re: Flagging an observation that is different from the previous one

Pmyosh — Mon, 25 Nov 2019 06:41:28 GMT

Hi,

You can use the LAG Function. If you want the value from the previous record, use LAG(variable).

If previous of previous record, use LAG2

Here's sample code

DATA sample;
	INPUT Subject  Event ;
DATALINES ;
1 1
1 2
1 3
1 4
1 5
1 5
1 6
;
RUN ;
DATA sample2 (Drop=Newx);
	SET sample ;
 	newx = LAG(EVENT) ;
	IF Event = newx THEN Flag = 'Y' ; ELSE Flag = 'N' ;
RUN ;