SPSSX Discussion

Re: do repeat

Posted by David Marso on
URL: http://spssx-discussion.165.s1.nabble.com/do-repeat-tp5719707p5719750.html

Art,
What is your concept of SYSMIS and do you think it should ever remain in a data file?
Isn't the very essence of system missing an entity that cannot be assigned a value by the 'system'?
I would consider division by zero as a candidate for treatment as SYSTEM MISSING rather than USER MISSING.

Interesting, you have been using SPSS 11 years longer than I have (1983).

However, I did spend 11 years working at SPSS in the trenches (6 doing teksport,5 as a Full time Consultant)- Teksport was existence in the belly of the beast-answering all sorts of 'exotic questions' (Macro, INPUT PROGRAM, MATRIX etc -yeah, all the weirdness that nobody else wanted to touch with a 10 foot pole- ).

In the early days of my taking on the 'exotic' I probably learned more from the users calling in than they learned from me. My very first exposure to macro was someone trying to do:
!LET !arg2=!arg1 + 1.
Well, that had me baffled. Well it is beyond obvious now, but believe it or not, once upon a time I was a rank newbie too.
I didn't pop out of my mother with a full blown SPSS manual in my brain ;-)

There was even a special folder in the support database called "Marso Madness". I wanted to call it "Doing Unnatural Acts with SPSS" but that got vetoed ;-).

I LEARNED what I know today by being exposed to all the weird things 'weird' people try to do with SPSS for 6 years, 8 hours a day.

I seriously doubt that support will even consider answering those sorts of questions any more. Maybe I'll call them for the heck of it and screw with their minds with some easy but actual 'how do I do this' question. and see how long it takes them to refer me to the consulting department ;-)))

Art Kendall wrote

I admit it is a soapbox
topic.

You surely are not a beginner and despite having used SPSS since
1972 I still learn from your posts.
However, people who follow the
list or search the archives are at least
to some degree learners.

To aid debugging and for
quality assurance review I try to have people catch
all instances of sysmis, redraft the syntax, and
provide for that condition in the transformations.
Then assign a missing value that can
be labelled.
Redrafting would not be finished
until all sysmis
had been changed to to user missing with
value labels
for example in this instance I would put
value labels varlist -999
'missing to avoid
dividing by zero' .

Art Kendall
Social Research Consultants
On 4/25/2013 1:47 PM, David Marso [via SPSSX Discussion] wrote:

In principle I agree with the sysmis on right side
for the most part.

However in this case it is a direct correlate to the notion that
the SYSTEM could NOT carry out some operation namely an attempted
division by 0 (which would indeed end up as SYSMIS in normal
calculations after spewing a host of warning messages. Protecting
the division with DO IF will render the same result. So, my using
SYSMIS in this case is deliberate and significant in reflecting
the inability of the system to caary out the computation.

--
In MATRIX such an misadventure results in a fatal untrappable
error and SPSS takes its ball and goes home (end of game), leading
to unhappy emails and or phone calls.

My shameless hack attempts to capitalize on the cranked up
energizer bunny properties of MATRIX vector efficiency while
gracefully avoiding division by 0. It is crucial to mop up
afterwards internally to avoid ludicrous results but it is easier
than protecting EVERY DIVISION in MATRIX with the following
awkward monstrosity.

DO IF (zero_check_matrix).

COMPUTE newarray = oldarray / value.

ELSE.

COMPUTE newarray=MAKE(NROW(oldarray),NCOL(oldArray),0).

LOOP #=1 TO NROW(oldarray).

LOOP ##=1 TO NCOL(oldArray).

COMPUTE newarray(#,##)=oldarray(#,##)/value.

END LOOP.

END LOOP.

END IF.

This also ends up being a PITA because one must take great care to
treat the resulting 0 appropriately in subsequent calculations.
In the HACK mode one can test for HUGE values which are
distinguishable from 0's which can legitimately arise from 0
numerators .

Yeah, there are trade offs, and I am nowhere near solving every
weird thing that can crop up in complex situations.

But, I do stand by my using SYSMIS for this situation ;-)

--

Art
Kendall wrote
OOPS! sysmis on
right side of

assignment operator.
RECODE ALL (LO THRU 1.0 = COPY)

(ELSE    -999    = ).

missing values all (-999).
Art Kendall

Social Research Consultants
On 4/25/2013 12:15 PM, Richard Ristow [via SPSSX
Discussion]

wrote:

At 09:43 AM 4/25/2013, David Marso wrote:

>If the numbers are all positive then you can nuke
the very

small fudge factor

>and remove the recode.

>If you have negative values then you will need to
modify the

recode (I'm

>sure you can sort that).

>RECODE ALL (1.000001 THRU HI=SYSMIS).

I think a cleaner way to do this RECODE, sidestepping
having to

choose a fudge factor, is

RECODE ALL (LO THRU 1.0 = COPY)

(ELSE = SYSMIS).

But actually, I think the dividing-by-zero problem is
a strong

reason

to do the computation in a transformation program,
rather than

MATRIX.

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Cum es damnatorum possederunt porcos iens ut salire off sanguinum cliff in abyssum?"