Scratch Variable

[Riya]

Dear SPSS Listers,

I am curious to know the meaning of ##. I understand scratch variable #. But what does this double pound sign ## mean? I mostly saw this in loop program.

[David Marso]

Riya,
  Can you provide the specific code?
It was most likely one of mine (or a copycat ;-).
In a 'normal' SPSS context # and ## will both be treated as scratch variables.
I use them mostly to indicate the level of the looping.
Say if I extended the IP below to 3 levels of nesting
I would likely use ### as the third level control variable.

In a MATRIX program there is no such notion but I use them to indicate they are throwaways and not of any significance to the solution aside from using them as indexes to Matrices.
In one case of note I am using #b, #b, #s, #t as controls within a matrix program
because the paper I am working with uses them in formulas.
If one used t as a variable MATRIX will render a funny error (t is short for TRANSPOSE).
Yeah, there's a method to my madness.
To anticipate another possible question?
The + in the first column of my code is just there for readability.
*--*.
INPUT PROGRAM.
+  VECTOR V (5).
+  LOOP #=1 TO 10.
+    LOOP ##=1 TO 5.
+      COMPUTE V(##)=RV.UNIFORM(0,#).
+    END LOOP.
+    END CASE.
+  END LOOP.
END FILE.
END INPUT PROGRAM.
FORMATS ALL (F10.5).
LIST.

        V1         V2         V3         V4         V5

    .45249     .30926     .60246     .44016     .23526
   1.25511     .81698     .04934     .21896    1.50149
    .28141    1.89411    1.80733    2.27208     .12114
   2.80992     .73832     .58700    1.68982    2.72828
   2.11903    4.97073     .34043    4.07132    3.14754
   1.89735     .13130    4.45608    2.95973     .57374
   2.17908    5.46643    2.35940    4.81436     .11513
   4.84745    4.00656    1.53321     .82136     .49609
   2.49844    8.80242    8.22399     .92355    4.65502
    .12636    8.09658    1.43747    8.94884    9.07983

*Number of cases read:  10    Number of cases listed:  10 *.

MATRIX .
COMPUTE V=UNIFORM(10,5).
LOOP #=1 TO 10.
+  LOOP ##=1 TO 5.
+    COMPUTE V(#,##) = V(#,##) * #.
+  END LOOP.
END LOOP.
PRINT V / FORMAT "F10.5" / TITLE "My little matrix that could?".
DISPLAY DICTIONARY.

END MATRIX.

Run MATRIX procedure:

My little matrix that could?
     .31061     .83313     .53507     .40160     .82489
    1.09797     .01224     .49796     .29495    1.53192
     .93221     .79862    2.10464    2.41575     .07050
    3.78063     .12584    1.14645    2.38256     .90979
     .35786    2.25725    4.17534    2.98023    3.04022
     .46606    3.11038     .49118    5.47010     .56301
    5.32857    1.56481    4.88623    3.75382     .67250
    5.14244    4.05917    1.81247    3.22525     .57517
    8.61627    8.67351    3.28237    1.97217    1.00668
    9.17098    4.07921    4.00496    8.37930    5.46965

Variables ---   Name             #Rows   #Columns
                V                   10          5
                #                    1          1
                ##                   1          1

------ END MATRIX -----

Riya wrote

Dear SPSS Listers,

I am curious to know the meaning of ##. I understand scratch variable #. But what does this double pound sign ## mean? I mostly saw this in loop program.

[Sarraf, Shimon Aaron]

I am currently out of the office until March 27. If you need immediate assistance, please call 812-856-5824.
Shimon Sarraf
Center for Postsecondary Research
Indiana University Bloomington

 

[Richard Ristow]

At 02:17 PM 3/25/2013, Riya wrote:

>I am curious to know the meaning of ##. I understand scratch
>variable #. But what does this double pound sign ## mean? I mostly
>saw this in loop program.

To expand on David's answer a little:

The character '#' is one of those accepted in any variable name:

>Variable names' first character must be a letter or one of the
>characters @, #, or $. Subsequent characters can be any combination
>of letters, numbers, a period (.), and non-punctuation characters.

'#' has a special meaning only as the first character of a name: it
specifies that the variable is a scratch variable. Otherwise, it's
just a character. So, if "a#" is of a normal variable, and "#a" is
the name of a scratch variable.

What names you use for scratch variables, apart from the first
character, is a matter of preference and aesthetics. As David notes,
he often uses the names "#", "##", and "###" for look counters. The
additional "#" characters are simply part of the name, and serve to
distinguish different variables; using, say, "#i", "#j", and "#k",
would serve the same purpose.

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