substract data from different rows

[mona4u]

Hi All, 

Below is an example of what I'm trying to achieve. My goal is to get the variable diff.  

X	Y	LAG	DIFF
1	A
2	A	1	1
3	A	2	1
4	A	3	1
5	A	4	1
1	B
2	B	1	1
3	B	2	1
4	B	3	1
5	B	4	1

Mona 

[Reeza]

Why is the first diff 1 when there's no previous value?
If it's always 1 why is this needed? It would be good to include a use case that illustrates a different scenario.

I suspect this is what you're after?

data want;
set have;
by y;
_dif = dif(x);
_lag = lag(x);
if first.y then call missing(_dif, _lag);
run;

---

@mona4u wrote:

Hi All, 

Below is an example of what I'm trying to achieve. My goal is to get the variable diff.  

X	Y	LAG	DIFF
1	A
2	A	1	1
3	A	2	1
4	A	3	1
5	A	4	1
1	B
2	B	1	1
3	B	2	1
4	B	3	1
5	B	4	1

Mona 

---

[mona4u]

because I don't want to subtract different group values. 

the diff value not always 1 this is just dummy 

[Reeza]

Did you try the code posted?

I'm assuming groups are defined by Y as you never stated. I'm assuming you want the lag of the variable X, also not specifically stated. 

If the above is true the answer should be correct. Use the DIF/LAG function and reset at the first of each group.