SPSS® 12.0 Command Syntax Reference

Example
DO REPEAT—END REPEAT 503
• The five variables are initialized to 0 by a single COMPUTE specification that is repeated
for each variable on the replacement list. Thus, the program generates five COMPUTE
commands from the one specified.
• Stand-in variable R ceases to exist once control passes out of the DO REPEAT structure.
* This example shows a typical application of INPUT PROGRAM, LOOP,
and DO REPEAT. A data file containing random numbers is generated.
INPUT PROGRAM.
+ LOOP #I = 1 TO 1000.
+ DO REPEAT RESPONSE = R1 TO R400.
+ COMPUTE RESPONSE = UNIFORM(1) > 0.5.
+ END REPEAT.
+ COMPUTE AVG = MEAN(R1 TO R400).
+ END CASE.
+ END LOOP.
+ END FILE.
END INPUT PROGRAM.
FREQUENCIES VARIABLE=AVG
/FORMAT=CONDENSE
/HISTOGRAM
/STATISTICS=MEAN MEDIAN MODE STDDEV MIN MAX.
• The INPUT PROGRAM—END INPUT PROGRAM structure encloses an input program that
builds cases from transformation commands.
• The indexing variable (#I) on LOOP—END LOOP indicates that the loop should be executed
1000 times.
• The DO REPEAT—END REPEAT structure generates 400 variables, each with a 50%
chance of being 0 and a 50% chance of being 1. This is accomplished by specifying a
logical expression on COMPUTE that compares the values returned by UNIFORM(1) to the
value 0.5. (UNIFORM(1) generates random numbers between 0 and 1.) Logical expressions
are evaluated as false (0), true (1), or missing. Thus, each random number returned
by UNIFORM that is 0.5 or less is evaluated as false and assigned the value 0, and each
random number returned by UNIFORM that is greater than 0.5 is evaluated as true and
assigned the value 1.
• The second COMPUTE creates variable AVG, which is the mean of R1 to R400 for each
case.
• END CASE builds a case with the variables created within each loop. Thus, the loop structure
creates 1000 cases, each with 401 variables (R1 to R400, and AVG).
• END FILE signals the end of the data file generated by the input program. If END FILE were
not specified in this example, the input program would go into an infinite loop. No
working file would be built, and the program would display an error message for every
procedure that follows the input program.
• FREQUENCIES produces a condensed frequency table, histogram, and statistics for AVG.
The histogram for AVG shows a normal distribution.