sum over paired observations

[natson001]

Supposed my dataset like this:

obs x

1     5

2     6

3     9

4     8

5     6

6     7

I want to replace the first obs with the sum of the first and the second (5 replayed by 5+6=11) and the third with the sum of the third and fourth (9 replace by 9+8=17) , etc.

The resulting dataset like this:

obs x

1    11

2    6

3    17

4     8

5     13

6     7

What is the best way to do that?

Thanks!

Andrew

[Reeza]

Why is the second and 4th left alone?

[natson001]

Because I want them to be there.

[Reeza]

Well if the logic is in your head then I guess you'll have to hard code it.  Seems kinda pointless then.

[PGStats · Accepted solution]

Strange but simple request... Here goes:

data have;

input obs x;

datalines;

1     5

2     6

3     9

4     8

5     6

6     7

;

data want;

if not end then set have(firstobs=2 rename=x=y) end=end;

set have;

if mod(_n_, 2) = 1 then x = x+y;

keep obs x;

run;

PG

[natson001]

Straightforward and beautiful! Thanks PG!

[stat_sas]

Another way to do it.

data want;
set have;
if mod(_n_,2) then flag+1;
run;

proc sql;
select obs,case when obs=min(obs) then sum(x) else x end as x from want
group by flag
order by obs;
quit;