Dif() function and first observation

[GKati]

data clients;

input client year cost;

datalines;

18 2011 589.92

18 2010 1629.8

18 2011 1813.29

18 2012 412.06

19 2012 219.82

20 2010 3669.98

20 2012 4879.63

;

run;

data work.client2;

set work.client;

dif_cost=dif(cost);

if first.client then dif_cost = . ;

run;

I get an error message that first.client is uninitialized. Why? My data is sorted by client and year. 

Thanks

[Astounding · Accepted solution]

Yes, your data is in order.  But that does not create FIRST. and LAST. variables.  To do that, you have to add the BY statement in the DATA step:

data work.client2;

set work.client;

by client;

The BY statement is what creates FIRST.CLIENT.  It doesn't put your data in order ... the data must be in order before the DATA step begins to make the BY statement legal.

[GKati]

Thank God for this forum! 🙂