Scratch Variables

You can use scratch variables to facilitate operations in transformation blocks and input programs.

• To create a scratch variable, specify a variable name that begins with the # character—for example, #ID. Scratch variables can be either numeric or string.
• Scratch variables are initialized to 0 for numeric variables or blank for string variables.
• Scratch variables cannot be used in procedures and cannot be saved in a data file (but they can be written to an external text file with PRINT or WRITE).
• Scratch variables cannot be assigned missing values, variable labels, or value labels.
• Scratch variables can be created between procedures but are always discarded as the next procedure begins.
• Scratch variables are discarded once a TEMPORARY command is specified.
• The keyword TO cannot refer to scratch variables and permanent variables at the same time.
• Scratch variables cannot be specified on a WEIGHT command.
• Scratch variable cannot be specified on the LEAVE command.
• Scratch variables are not reinitialized when a new case is read. Their values are always carried across cases. (So using a scratch variable can be essentially equivalent to using the LEAVE command.)

Because scratch variables are discarded, they are often useful as loop index variables and as other variables that do not need to be retained at the end of a transformation block. See the topic Indexing Clause (LOOP-END LOOP command) for more information. Because scratch variables are not reinitialized for each case, they are also useful in loops that span cases in an input program. See the topic Creating Data (LOOP-END LOOP command) for more information.

Example

DATA LIST LIST (",") /Name (A15).
BEGIN DATA
Nick Lowe
Dave Edmunds
END DATA.
STRING LastName (A15).
COMPUTE #index=INDEX(Name, " ").
COMPUTE LastName=SUBSTR(Name, #index+1).
LIST.

Name            LastName

Nick Lowe       Lowe
Dave Edmunds    Edmunds

• #index is a scratch variable that is set to the numeric position of the first occurrence of a blank space in Name.
• The scratch variable is then used in the second COMPUTE command to determine the starting position of LastName within Name.
• The default LIST command will list the values of all variables for all cases. It does not include #index because LIST is a procedure that reads the data, and all scratch variables are discarded at that point.

In this example, you could have obtained the same end result without the scratch variable, using:

COMPUTE LastName=SUBSTR(Name, INDEX(Name, " ")+1).

The use of a scratch variable here simply makes the code easier to read.

Example: Scratch variable initialization

DATA LIST FREE /Var1.
BEGIN DATA
2 2 2
END DATA.
COMPUTE Var2=Var1+Var2.
COMPUTE Var3=0.
COMPUTE Var3=Var1+Var3.
COMPUTE #ScratchVar=Var1+#ScratchVar.
COMPUTE Var4=#ScratchVar.
LIST.

    Var1     Var2     Var3     Var4

    2.00      .       2.00     2.00
    2.00      .       2.00     4.00
    2.00      .       2.00     6.00

• The new variable Var2 is reinitialized to system-missing for each case, therefore Var1+Var2 always results in system-missing.
• The new variable Var3 is reset to 0 for each case (COMPUTE Var3=0), therefore Var1+Var3 is always equivalent to Var1+0.
• #ScratchVar is initialized to 0 for the first case and is not reinitialized for subsequent cases; so Var1+#ScratchVar is equivalent to Var1+0 for the first case, Var1+2 for the second case, and Var1+4 for the third case.
• Var4 is set to the value of #ScratchVar in this example so that the value can be displayed in the case listing.

In this example, the commands:

COMPUTE #ScratchVar=Var1+#ScratchVar. 
COMPUTE Var4=#ScratchVar.

are equivalent to:

COMPUTE Var4=Var1+Var4.
LEAVE Var4.