SPSS® 12.0 Command Syntax Reference

LOOP—END LOOP
LOOP [varname=n TO m [BY {1**}]] [IF [(]logical expression[)]]
{n }
transformation commands
END LOOP [IF [(]logical expression[)]]
**Default if the subcommand is omitted.
Examples
SET MXLOOPS=10. /*Maximum number of loops allowed
LOOP. /*Loop with no limit other than MXLOOPS
COMPUTE X=X+1.
END LOOP.
LOOP #I=1 TO 5. /*Loop five times
COMPUTE X=X+1.
END LOOP.
Overview
The LOOP—END LOOP structure performs repeated transformations specified by the commands
within the loop until they reach a specified cutoff. The cutoff can be specified by an
indexing clause on the LOOP command, an IF clause on the END LOOP command, or a
BREAK command within the loop structure (see BREAK). In addition, the maximum number
of iterations within a loop can be specified on the MXLOOPS subcommand on SET. The
default MXLOOPS is 40.
The IF clause on the LOOP command can be used to perform repeated transformations
on a subset of cases. The effect is similar to nesting the LOOP—END LOOP structure within
a DO IF—END IF structure, but using IF on LOOP is simpler and more efficient. You have to
use the DO IF—END IF structure, however, if you want to perform different transformations
on different subsets of cases. You can also use IF on LOOP to specify the cutoff, especially
when the cutoff may be reached before the first iteration.
LOOP and END LOOP are usually used within an input program or with the VECTOR command.
Since the loop structure repeats transformations on a single case or on a single input
record containing information on multiple cases, it allows you to read complex data files or
to generate data for a working data file. For more information, see INPUT PROGRAM—END
INPUT PROGRAM and VECTOR.
The loop structure repeats transformations on single cases across variables. It is different
from the DO REPEAT—END REPEAT structure, which replicates transformations on a
specified set of variables. When both can be used to accomplish a task, such as selectively
transforming data for some cases on some variables, LOOP and END LOOP are generally
more efficient and more flexible, but DO REPEAT allows selection of nonadjacent variables
and use of replacement values with different intervals.
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