SPSS® 12.0 Command Syntax Reference

LOOP—END LOOP 837
• The loop is executed once for a case with Y equal to 2 and Z equal to 2 but twice for a case
with Y equal to 3 and Z equal to 2.
Example
* Repeating data using LOOP.
INPUT PROGRAM.
DATA LIST NOTABLE/ ORDER 1-4(N) #BKINFO 6-71(A).
LEAVE ORDER.
LOOP #I = 1 TO 66 BY 6 IF SUBSTR(#BKINFO,#I,6) ’ ’.
+ REREAD COLUMN = #I+5.
+ DATA LIST NOTABLE/ ISBN 1-3(N) QUANTITY 4-5.
+ END CASE.
END LOOP.
END INPUT PROGRAM.
SORT CASES BY ISBN ORDER.
BEGIN DATA
1045 182 2 155 1 134 1 153 5
1046 155 3 153 5 163 1
1047 161 5 182 2 163 4 186 6
1048 186 2
1049 155 2 163 2 153 2 074 1 161 1
END DATA.
DO IF $CASENUM = 1.
+ PRINT EJECT /’Order’ 1 ’ISBN’ 7 ’Quantity’ 13.
END IF.
PRINT /ORDER 2-5(N) ISBN 8-10(N) QUANTITY 13-17.
EXECUTE.
• This example uses LOOP to simulate a REPEATING DATA command.
• DATA LIST specifies the scratch variable #BKINFO as a string variable (format A) to allow
blanks in the data.
• LOOP is executed if the SUBSTR function returns anything other than a blank or null
value. SUBSTR returns a six-character substring of #BKINFO, beginning with the character
in the position specified by the value of the indexing variable #I. As specified on the
indexing clause, #I begins with a value of 1 and is increased by 6 for each iteration of
LOOP, up to a maximum #I value of 61 (1 + 10 × 6 = 61). The next iteration would exceed
the maximum #I value (1 + 11 × 6 = 67).
Missing Values
• If the program encounters a case with a missing value for the initial, terminal, or increment
value or expression, or if the conditional expression on the LOOP command returns
missing, a zero-trip loop results and control is passed to the first command after the END
LOOP command.
• If a case has a missing value for the conditional expression on an END LOOP command,
the loop is terminated after the first iteration.
• To prevent cases with missing values for any variable used in the loop structure from
entering the loop, use the IF clause on the LOOP command (see third example below).