quick question

[Hoover, Matthew]

Hello everyone,

 

I know that people tend to overuse the "execute" command and that can
really slow down data processing, but I'm unsure of what procedures
require an execute command.  For example, for code like this:

 

DO IF (SYSMIS(gradef03)).

COMPUTE gradef03=d_grf03.

END IF.

EXECUTE.

 

DO IF (SYSMIS(grades04)).

COMPUTE grades04=d_grs04.

END IF.

EXECUTE.

 

Could I re-write this as?

 

DO IF (SYSMIS(gradef03)).

COMPUTE gradef03=d_grf03.

END IF.

 

DO IF (SYSMIS(grades04)).

COMPUTE grades04=d_grs04.

END IF.

 

Will SPSS automatically run execute commands when it needs to calculate
a value for a new variable (therefore, you can eliminate them completely
in syntax except perhaps at the end)?

 

Thanks

 

Matt (still an SPSS newbie in many ways).

 

 

[Justin Black]

Hi Matt,

Other, more experienced users may have different recommendations for more
efficient ways to do what you're trying to do, but using the syntax below
will reduce the number of required transformations and should give you the
same results as the DO IF's you're using currently.

IF (SYSMIS(gradef03)) gradef03=d_grf03 .
IF (SYSMIS(grades04)) grades04=d_grs04 .
EXE .

Hope that helps!

--Justin

--
Justin Black
Doctoral Student in Residence
Industrial-Organizational Psychology
Baruch College, CUNY
Box B 8-215
One Bernard Baruch Way
New York, NY 10010
Tel: [phone]
fax. [phone]

On 9/27/06, Hoover, Matthew <[hidden email]> wrote:

>
> Hello everyone,
>
>
>
> I know that people tend to overuse the "execute" command and that can
> really slow down data processing, but I'm unsure of what procedures
> require an execute command.  For example, for code like this:
>
>
>
> DO IF (SYSMIS(gradef03)).
>
> COMPUTE gradef03=d_grf03.
>
> END IF.
>
> EXECUTE.
>
>
>
> DO IF (SYSMIS(grades04)).
>
> COMPUTE grades04=d_grs04.
>
> END IF.
>
> EXECUTE.
>
>
>
> Could I re-write this as?
>
>
>
> DO IF (SYSMIS(gradef03)).
>
> COMPUTE gradef03=d_grf03.
>
> END IF.
>
>
>
> DO IF (SYSMIS(grades04)).
>
> COMPUTE grades04=d_grs04.
>
> END IF.
>
>
>
> Will SPSS automatically run execute commands when it needs to calculate
> a value for a new variable (therefore, you can eliminate them completely
> in syntax except perhaps at the end)?
>
>
>
> Thanks
>
>
>
> Matt (still an SPSS newbie in many ways).
>
>
>
>
>

[Gary Rosin]

Matthew Hoover wrote:

>I know that people tend to overuse the "execute" command and
>that can really slow down data processing, but I'm unsure of what
>procedures require an execute command.  * * *
>
>* * *
>
>Will SPSS automatically run execute commands when it needs
>to calculate a value for a new variable (therefore, you can eliminate
>them completely in syntax except perhaps at the end)?


I believe SPSS executes commands when necessary to generate
a variable so it can be used, but not until then.  At least when using
a Python script to submit commands, I found that I was left with a
"transformation pending" unless I submitted an 'EXECUTE" command
at the end.  If you're only running a syntax file, you may not need to.

Gary

[Peck, Jon]

EXECUTE  is only needed in a few esoteric cases.  No procedure requires an EXECUTE

For the Python comment below, Submit does what you tell it.  It does not automatically add an execute, but if you ran a procedure in the regular way after the program, the generated transformations would be executed "just in time".

Regards,
Jon Peck

-----Original Message-----
From: SPSSX(r) Discussion [mailto:[hidden email]] On Behalf Of Gary Rosin
Sent: Wednesday, September 27, 2006 11:43 AM
To: [hidden email]
Subject: Re: [SPSSX-L] quick question

Matthew Hoover wrote:

>I know that people tend to overuse the "execute" command and
>that can really slow down data processing, but I'm unsure of what
>procedures require an execute command.  * * *
>
>* * *
>
>Will SPSS automatically run execute commands when it needs
>to calculate a value for a new variable (therefore, you can eliminate
>them completely in syntax except perhaps at the end)?


I believe SPSS executes commands when necessary to generate
a variable so it can be used, but not until then.  At least when using
a Python script to submit commands, I found that I was left with a
"transformation pending" unless I submitted an 'EXECUTE" command
at the end.  If you're only running a syntax file, you may not need to.

Gary

[Hal 9000]

My mental checklist for using .exe is:

a.) immediate after the lag function is used to compute a var
b.) after writing out to an .sps file and before inserting that file within
the same syntax
c.) before using the delete vars command

Am I missing any biggies?

[Richard Ristow]

OK, you knew you were waving a red flag at THIS bull (grin).

At 10:42 AM 9/27/2006, Hoover, Matthew wrote:

>I'm unsure of what procedures require an execute
>command.  For example, for code like this:
>
>
>DO IF (SYSMIS(gradef03)).
>.  COMPUTE gradef03=d_grf03.
>END IF.
>EXECUTE.
>
>DO IF (SYSMIS(grades04)).
>.  COMPUTE grades04=d_grs04.
>END IF.
>EXECUTE.
>
>Could I re-write this [without either EXECUTE]?

Yes, you could; it would work fine, and faster.

By way of a short tutorial, and skipping Python
(it's just in the way, for this discussion), the
standard order of SPSS programs is a
'transformation program' followed by a
'procedure', then another transformation program and procedure, etc.

(Before this starts, there needs to be a file, so
there needs to be a command that defines one:
DATA LIST, GET FILE, MATCH FILES, ...)

The transformation program is made up of
transformation commands: COMPUTE, IF, RECODE, DO
IF, LOOP, ...  They explicitly define the values,
or properties, of variables.

The 'procedures' are the statistical and
reporting commands: FREQUENCIES, REGRESSION, all
the others. EXECUTE is a procedure. Procedures
use the whole file, and require that the whole
file be read. Transformation programs work on a
case (or record) at a time; the program is
'handed' one case at a time, does its work, and
'hands' the result to the procedure, until the
procedure has 'seen' the whole file.

If you write

COMPUTE C = A + B.
EXECUTE.
COMPUTE D = C * E.

then the first COMPUTE statement is a
transformation program by itself. For each record
of the file, it computes the new value of C, then
passes the record to EXECUTE (which does nothing
with it). The new values of C remain in the file,
and the second COMPUTE, which is also a
transformation program, 'sees' the new values and them to compute D.

If you leave out the EXECUTE, and write

COMPUTE C = A + B.
COMPUTE D = C * E.

then the two COMPUTEs together are a single
transformation program. For each record, the
program first computes the new value of C; then,
using that new value, it computes the new value
of D; then, it passes that record to whatever procedure follows.

Put in EXECUTE, and SPSS runs through the file
doing the first computation, then again doing the
second. Leave it out, and it runs through once,
doing both computations.

(Think of the file as a table, with the variables
being columns, and the cases or records being
rows. If you have an EXECUTE between those
COMPUTEs, SPSS moves down the rows making the
first computation; then, starts back at the top
and makes the second. If you have no EXECUTE,
SPSS moves *once* down the rows, making all the
computations row by row.)

Now, to comment on comments:

>using the syntax below will reduce the number of
>required transformations and should give you the
>same results as the DO IF's you're using currently.
>
>IF (SYSMIS(gradef03)) gradef03=d_grf03 .
>IF (SYSMIS(grades04)) grades04=d_grs04 .
>EXE .

It will give the same results. It is fewer
transformation lines than using the DO IFs, but
which you prefer is mainly taste; you'll never
see any difference in the speed. But this "EXE."
is not needed, either; it, too, reads the whole
file to no purpose. The next procedure, or SAVE
FILE, will cause the file to be read and the computations performed.

>>Will SPSS automatically run execute commands
>>when it needs to calculate a value for a new
>>variable (therefore, you can eliminate them
>>completely in syntax except perhaps at the end)?
>
>I believe SPSS executes commands when necessary
>to generate a variable so it can be used, but not until then.

That last is it. It isn't that SPSS runs
'EXECUTE' commands; it's that it doesn't need
them. SPSS runs the whole transformation program
when it 'needs' the results: for a procedure, or a SAVE.

>My mental checklist for using .exe is:
>
>a.) immediate after the lag function is used to compute a var

No; almost never needed. If you use the lagged
value of a variable WHICH IS MODIFIED IN THE SAME
TRANSFORMATION PROGRAM, then EXECUTE may be
needed; see section "Use EXECUTE sparingly" in Raynald Levesque's book.

>b.) after writing out to an .sps file and before
>inserting that file within the same syntax

Yes, but it may not be for the reason you're
thinking. If you're using PRINT or WRITE or XSAVE
in a transformation program, they won't be
executed until the transformation program is run,
which is concurrently with the next procedure.
You do need the do-nothing procedure "EXECUTE" to
cause the transformation program to be run and
the results made available.

>c.) before using the delete vars command

That's needed; DELETE VARS needs to be at the
head of a transformation program. However, you
can almost always rearrange your logic to avoid
the EXECUTE; for example, put DELETE VARS
directly after the next procedure you were going to run anyway.

Finally, do see "Use EXECUTE Sparingly" in Raynald Levesque's book:
Levesque, Raynald, "SPSS® Programming and Data
Management, 3rd Edition/A Guide for SPSS® and
SAS® Users". SPSS, Inc., Chicago, IL, 2005.

You can download it free as a PDF file, from
http://www.spss.com/spss/SPSS_programming_data_mgmt.pdf.

(The third edition includes a lot on Python
programming. For any SPSS version earlier 14, the
second edition will be at least as good.)

.......
Cheers, and onward. My apologies for any place
I'm not clear - a tutorial may not come out
right, the first time you write it.