Date: Sun, 23 Jan 2005 18:03:15 -0800
Reply-To: Howie Harshaw <harshaw@interchange.ubc.ca>
Sender: "SPSSX(r) Discussion" <SPSSX-L@LISTSERV.UGA.EDU>
From: Howie Harshaw <harshaw@interchange.ubc.ca>
Subject: Re: DO IF ELSE syntax question
In-Reply-To: <5.1.0.14.2.20050123185204.067a9920@pop.mindspring.com>
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Thank you Richard for cleaning up and correcting my syntax - with a
slight modification (below in the 3rd ELSE IF statement) it runs
perfectly. Thanks too for the walk through SPSS logic - I have a better
understanding of why what I was doing wasn't working, and will follow up
with the syntax manual as you suggest.
- Howie
DO IF (NMISS(recimp1r,recimp2r,recimp3r) = 3).
. Compute rec_spec1 = 0.
ELSE IF (NMISS(recimp1r,recimp2r,recimp3r) = 0).
. Compute rec_spec1 = 1.
ELSE IF ((NOT MISSING(recimp1r)) AND (NOT MISSING(recimp2r)) AND
(MISSING(recimp3r))).
. Compute rec_spec1 = 2.
ELSE IF ((NOT MISSING(recimp1r)) AND (MISSING(recimp2r)) AND
(MISSING(recimp3r))).
. Compute rec_spec1 = 3.
END IF.
EXECUTE.
_______________________________
Howard Harshaw
Ph.D. Candidate
Forest Resource Management
Faculty of Forestry
University of British Columbia
Tel: (604) 786-3141
E-mail: harshaw@interchange.ubc.ca
Web: www.Harfolk.ca
Richard Ristow wrote:
> This is the beginning of an answer. What you're trying to do is
> reasonable, but there are several problems with how you're trying to do it.
>
> At 05:07 PM 1/23/2005, Howie Harshaw wrote:
>
>> I have four numeric variables:
>> recimp1r: values = 1-45; 999 = user missing
>> recimp2r: values = 1-45; 999 = user missing
>> recimp3r: values = 1-45; 999 = user missing
>> rec_spec1 (empty)
>>
>> I would like to assign,
>> "0" to rec_spec1 if recimp1r, recimp2r, and recimp3r all contain
>> missing values (i.e. 999);
>> "1" to rec_spec1 if recimp1r, recimp2r, and recimp3r do not contain
>> missing values (i.e. 999) [QUESTION: That is, if none of them do?];
>> "2" to rec_spec1 if recimp1r and recimp2r do not contain missing
>> values (i.e. 999) but recimp3r does;
>> "3" to rec_spec1 if recimp1r does not contain missing values (i.e.
>> 999) but and recimp2r recimp3r do.
>
>
> Let me try it in pieces. Before I start, you'll see below that I've
> written lines like this:
> . Compute rec_spec1 = 0.
> or like this:
> - DO IF (NMISS(recimp1r,recimp2r,recimp3r)=3).
> Those are indents. If you start an SPSS command line with "." or "-",
> you can put in as many spaces as you like before the keyword. Those
> statements are the same as
> Compute rec_spec1 = 0.
> DO IF (NMISS(recimp1r,recimp2r,recimp3r)=3).
>
> But now, to your problem. You begin with,
>
>> DO IF ((recimp1r = 999 AND recimp2r = 999) AND recimp3r = 999).
>> . Compute rec_spec1 = 0.
>
>
> This isn't causing the problem you're seeing, but it won't work, either.
> With your data, the tests "recimp1r=999", etc., will *NEVER* be true.
> Remember, 999 is a missing value. If recimpr1r is 999, SPSS will
> interpret it as "value of recimpr1r unknown", and the result is
> "missing". ("Missing" is neither 'true' nor 'false'.)
>
> The following variations will work:
> GOOD (if the variables are never system-missing):
> - DO IF ((VALUE(recimp1r) = 999 AND VALUE(recimp2r) = 999)
> AND VALUE(recimp3r) = 999).
> . Compute rec_spec1 = 0.
> BETTER (will detect both '999' and system-missing):
> - DO IF ((MISSING(recimp1r) AND MISSING(recimp2r)
> AND MISSING(recimp3r)).
> . Compute rec_spec1 = 0.
> BEST (will detect both '999' and system-missing):
> - DO IF (NMISS(recimp1r,recimp2r,recimp3r)=3).
> . Compute rec_spec1 = 0.
>
>> ELSE.
>> IF ((recimp1r <> 999 AND recimp2r <> 999) AND recimp3r <> 999).
>> . Compute rec_spec1 = 1.
>
>
> This may be the problem you're seeing. If you mean "ELSE IF", that is a
> *single* statement. You have two statements:
> ELSE.
> IF <test>.
>
> This has a meaning, but probably not the one you want. So,
> - ELSE IF ((recimp1r <> 999 AND recimp2r <> 999) AND recimp3r <> 999).
> . Compute rec_spec1 = 1.
>
> But that won't work if any of the values is 999. A good alternative is
> - ELSE IF (NMISS(recimp1r,recimp2r,recimp3r) = 0).
> . Compute rec_spec1 = 1.
>
> But, to go back to where you were. You have,
>
>> ELSE.
>> IF ((recimp1r <> 999 AND recimp2r <> 999) AND recimp3r <> 999).
>> . Compute rec_spec1 = 1.
>
>
> There is a statement named "IF". It performs a test and an assignment
> (like a "COMPUTE") together. Syntax (from the syntax manual) is,
> IF [(]logical expression[)] target variable=expression
> (The square brackets mean you can put the parentheses in, or leave them
> out.)
>
> I think that
> . IF ((recimp1r <> 999 AND recimp2r <> 999) AND recimp3r <> 999).
> is giving you the error message.
>
>> >Error # 4382 in column 256. Text: (End of Command)
>> >An equals sign was not found when expected after a target variable in a
>> >COMPUTE command.
>> >This command not executed.
>
>
> You have an "IF" statement with the test, but without
> "variable=expression", and that's confusing SPSS.
>
> In the syntax manual, you should read, carefully,
> . "Missing Values in Logical Expressions", in section "Transformation
> Expressions", near the beginning (but, I'm afraid, it's not as clear as
> one would like)
> . The section on IF
> . The section on DO IF. In particular, try read the following until it
> makes sense. (And do not be afraid to post further questions.):
> "Flow of Control
> "· If the logical expression on DO IF is true, the commands immediately
> following DO IF are executed up to the next ELSE IF or ELSE or END IF
> command. Control then passes to the first statement following END IF.
> "· If the expression on DO IF is false, control passes to the following
> ELSE IF command. Multiple ELSE IF commands are evaluated in the order in
> which they are specified until the logical expression on one of them is
> true. Commands following that ELSE IF command are executed up to the
> ELSE or END IF command, and control passes to the first statement
> following END IF.
> "· If none of the expressions are true on the DO IF or any of the ELSE
> IF commands, the commands following ELSE are executed and control passes
> out of the structure. If there is no ELSE command, a case goes through
> the entire structure with no change.
> "· [THIS IS THE TRICKY ONE] Missing values returned by the logical
> expression on DO IF or on any ELSE IF cause control to pass to the END
> IF command at that point[, that is, to skip the rest of the DO IF
> structure]."
>
> In the meantime, this should work (but I have not tested it):
>
> DO IF (NMISS(recimp1r,recimp2r,recimp3r) = 3).
> . Compute rec_spec1 = 0.
> ELSE IF (NMISS(recimp1r,recimp2r,recimp3r) = 0.
> . Compute rec_spec1 = 1.
> ELSE IF ((NOT MISSING(recimp1r)) AND (NOT MISSING(recimp2r))
> AND (MISSING(recimp3r))).
> . Compute rec_spec1 = 2.
> ELSE IF ( (MISSING(recimp1r)) AND (MISSING(recimp2r))
> AND (NOT MISSING(recimp3r))999).
> . Compute rec_spec1 = 3.
> END IF.
>
>
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