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On Fri, Apr 11, 2008 at 7:44 PM, AnoniDeer <irain168@gmail.com> wrote:
> I have a dataset like this.How could I get the difference between the
> third and fourth observations for each of the group? for example for
> the group 1 I need to get the difference for the observation of 45 and
> 34. For the second group I need the difference of 76-34 and so on...
> How to write a program to realize this? Thanks so much!
>
> group x
> 1 23
> 1 .
> 1 34
> 1 45
> 2 45
> 2 89
> 2 34
> 2 76
> 4 23
> 4 12
> 4 23
> 4 12
>
Here is a lengthy program. It does not assume that there should be 4
observations per group and that they need be together within group. Hash
object is used to sense the group change. When the 3rd and 4th observations
within a group are met they are used to find the difference and saved to
output data set.
data have;
input group x;
cards;
1 23
1 .
1 34
1 45
2 45
2 89
2 34
2 76
4 23
4 12
4 23
4 12
;
run;
data need;
if _n_ = 1 then do;
if 0 then set have;
declare hash h();
h.definekey('group');
h.definedone();
end;
do until(eof);
set have end = eof;
if h.find() ne 0 then do;
count = 1;
x3 = 0;
h.add();
end;
else do;
count ++ 1;
if count = 3 then x3 = x;
if count = 4 then do;
x_34 = x - x3;
output;
end;
end;
end;
stop;
drop count x3;
run;
proc print data = need;
run;
Muthia Kachirayan
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