```Date: Thu, 31 Oct 2002 16:54:04 -0600 Reply-To: "Peck, Jon" Sender: "SPSSX(r) Discussion" From: "Peck, Jon" Subject: Re: Why does (missing value) multiplied by zero = zero? Comments: To: Andrew Fenyo Content-Type: text/plain; charset="iso-8859-1" The SPSS Syntax Reference explains what is happening here... Some arithmetic operations involving 0 can be evaluated even when the variables have missing values. These operations are 0*missing = 0 0/missing = 0 mod(0,missing) = 0 ---------- You can use the SYSMIS() or MISSING() functions in an expression to achieve different results. Regards, Jon Peck -----Original Message----- From: Andrew Fenyo [mailto:A.J.Fenyo@ukc.ac.uk] Sent: Thursday, October 31, 2002 11:27 AM To: SPSSX-L@LISTSERV.UGA.EDU Subject: [SPSSX-L] Why does (missing value) multiplied by zero = zero? Folks, I have been tearing my hair out, but I cannot see what I am doing wrong! I have a variable Q and a category TYPE. I need to create two new variables (QA and QB) which take the value of Q or MISSING depending on TYPE. It works fine EXCEPT when Q is zero: then I get both QA and QB set to zero. I have probably overlooked something very simple, but any suggestions would be most welcome. Here is a sample and the syntax: DATA LIST LIST /TYPE Q. BEGIN DATA 1 25 1 2 1 0 1 6 1 17 2 6 2 26 2 9999 2 0 2 18 END DATA. LIST. MISSING VALUES Q (9999). COMPUTE ATYPE=2-TYPE. COMPUTE BTYPE=1-ATYPE. MISSING VALUES ATYPE BTYPE (0). LIST. DO IF MISSING (Q). COMPUTE QA=-9. COMPUTE QB=-9. ELSE. COMPUTE QA=Q*ATYPE. COMPUTE QB=Q*BTYPE. END IF. MISSING VALUES QA QB (-9). LIST. ============================== Andrew Fenyo, Senior Computing Officer Personal Social Services Research Unit University of Kent, Canterbury, CT2 7NF Voice: 01227 827610 Fax: 01227 827038 PSSRU: http://www.ukc.ac.uk/PSSRU ```

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