Date:         Wed, 21 Apr 1999 14:29:23 GMT
Reply-To:     wenyu1030@MY-DEJANEWS.COM
Sender:       "SAS(r) Discussion" <SAS-L@UGA.CC.UGA.EDU>
From:         wenyu1030@MY-DEJANEWS.COM
Organization: Deja News - The Leader in Internet Discussion
Subject:      How to dedect frequent sign changes

Hi,
 
I am trying to write an efficient SAS code to handle the following question.
 
Suppose I have a SAS dataset created with ID number and a variable x.
Observations of x consist of consecutive positive numbers followed by
consecutive negative numbers, and then maybe consecutive positive numbers
again. in fact, this is a large data set so such sign changes may occur more
than a number of times. The dataset may look something like this:
 
 
1 2
2 3
3 -1
4 -2
5 7
6 8
7 -9
8 -9
 
What I want to do is to output the observation whenever its sign changes,
i.e., its sign is different from its previous one----such as observation 3, 5,
and 7 in the above dataset.
 
Can somebody suggest an efficient code for solving this problem?
 
Thanks.
 
wenyu
 
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