how to map to the previous variable value??

[GeethaMN]

can anyone answer this query??

there is a input variable called X. need to derive variable called 'Y'.. the scenario is wherever there is 999 value there it has to add 0.1 to the previous x value.. if more than one 999 is there then the order should be 3.1, 3.2,3.3

X        Y

1        1
2        2
3        3
4        4
999    4.1
1        1
2        2
3        3
999    3.1
999    3.2

[Reeza]

Use the lag function. 

X_lag = lag(X);
Y=ifn(X=999, x_lag+0.1, X);

This doesn't deal with consecutive 999 so you'll need to figure out the logic for that.  

[Ksharp]

data have;
input X ;
cards; 
1      
2      
3   
4  
999  
1   
2  
3    
999 
999   
;
run;

data want;
 set have;
 retain Y;
 if X ne 999 then Y=X;
  else Y=Y+0.1;
run;

[Ksharp]

Or more simple :

data want;
 set have;
 if X ne 999 then Y=X;
  else Y+0.1;
run;