Flagging an observation that is different from the previous one

[Dregerator]

Hi

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           A

1           C

1           A

1           B

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?

[PeterClemmensen · Accepted solution]

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 

[Pmyosh]

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 ;