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You certainly can't manipulate it the way you suggest directly, as that
would be inconsistent with how a data step works.
The ways I could imagine doing something like that:
-- Use a counter:
data
have;
input id
x;
cards;
1
1
1
1
1
3
1
4
2
1
2
2
2
3
3
2
3
3
3
4
;
run;
proc sort
data=have;
by
id;
run;
data
have2;
set
have;
by
id;
if first.id then
counter=0;
counter+1;
run;
data
want;
set
have2;
by
id;
retain
firstid;
if first.id then
firstid=1;
if counter = firstid then
do;
if x eq 1 then
do;
firstid=firstid+1;
delete;
end;
end;
run;
*yields 7 records, deleting the first two records in id=1 and the first
record in id=2.
-- Use a retained tracker (same HAVE dataset):
data
want;
set
have;
by
id;
retain
nodelete;
if first.id then
nodelete=0;
if nodelete=0 then
do;
if x eq 1 then
do;
delete;
end;
else
nodelete=1;
end;
run;
-- DOW loop:
data
want;
do y=1 by 1 until (last.id or x ne
1);
set
have;
by
id;
end;
drop
y;
run;
though I'm not 100% sure why this works, I was expecting it to not work at
all, but it at least works for the example (and also for the example where
x=1 further down from first.id, it keeps that record). But it does seem to
work.
-- Perhaps use LAG, though I can't come up with a functional example.
-Joe
On Wed, Jan 28, 2009 at 6:06 PM, Arthur Tabachneck <art297@netscape.net>wrote:
> Akshaya asked a question earlier today that made me think of a solution
> that required a manipulative first.variable feature. However, I don't
> know how one could accomplish that. For example, given the data file:
>
> data have;
> input id x;
> cards;
> 1 1
> 1 2
> 1 3
> 1 4
> 2 1
> 2 2
> 2 3
> 3 2
> 3 3
> 3 4
> ;
>
> how can one, or can one, reset first.id if, because of a delete, it isn't
> the first record anymore? For example:
>
> data want;
> set test;
> by id;
> if first.id then do;
> if x eq 1 then do;
> delete;
> /* reset first.id here*/;
> end;
> end;
> first_id=first.id;
> run;
>
> would (if the missing command were added) end up looking like:
>
> data desired_want;
> input id x first_id;
> cards;
> 1 2 1
> 1 3 0
> 1 4 0
> 2 2 1
> 2 3 0
> 3 2 1
> 3 3 0
> 3 4 0
> ;
>
> Just wondering,
> Art
>
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