SPSS® 12.0 Command Syntax Reference

834 LOOP—END LOOP
Example
* Factorial routine.
DATA LIST FREE / X.
BEGIN DATA
1 2 3 4 5 6 7
END DATA.
COMPUTE FACTOR=1.
LOOP #I=1 TO X.
COMPUTE FACTOR=FACTOR * #I.
END LOOP.
LIST.
• The loop structure computes FACTOR as the factorial value of X.
Example
* Example of nested loops: compute every possible combination of values
for each variable.
INPUT PROGRAM.
-LOOP #I=1 TO 4. /* LOOP TO NUMBER OF VALUES FOR I
+ LOOP #J=1 TO 3. /* LOOP TO NUMBER OF VALUES FOR J
@ LOOP #K=1 TO 4. /* LOOP TO NUMBER OF VALUES FOR K
@ COMPUTE I=#I.
@ COMPUTE J=#J.
@ COMPUTE K=#K.
@ END CASE.
@ END LOOP.
+ END LOOP.
-END LOOP.
END FILE.
END INPUT PROGRAM.
LIST.
• The first loop iterates four times. The first iteration sets the indexing variable #I equal to
1 and then passes control to the second loop. #I remains 1 until the second loop has completed
all of its iterations.
• The second loop is executed 12 times, three times for each value of #I. The first iteration
sets the indexing variable #J equal to 1 and then passes control to the third loop. #J remains
1 until the third loop has completed all of its iterations.
• The third loop results in 48 iterations (4 × 3 × 4). The first iteration sets #K equal to 1. The
COMPUTE statements set the variables I, J, and K each to 1, and END CASE creates a case.
The third loop iterates a second time, setting #K equal to 2. Variables I, J, and K are then
computed with values 1, 1, 2, respectively, and a second case is created. The third and
fourth iterations of the third loop produce cases with I, J, and K, equal to 1, 1, 3 and 1, 1,
4, respectively. After the fourth iteration within the third loop, control passes back to the
second loop.
• The second loop is executed again. #I remains 1, while #J increases to 2, and control returns
to the third loop. The third loop completes its iterations, resulting in four more cases
with I equal to 1, J to 2, and K increasing from 1 to 4. The second loop is executed a third