SAS BASE 考试题请教Chapter 21 quiz 4th

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收藏 2016-08-03

请教下各位，以下这道题看了好多遍，始终觉得应该是第五次iteration就会出现答案B的效果，为啥题目说是in the sixth iteration？英文不太好，求教了。谢谢！

After the value for code is read in the sixth iteration, which illustration of the program data vector is correct?

1---+----10---+----20---+----30

H Lettuce

P Green Leaf Quality Growers

P Iceberg Pleasant Farm

P Romaine Quality Growers

H Squash

P Yellow Tasty Acres

P Zucchini Pleasant Farm

data perm.produce (drop=code); infile orders; retain Vegetable; input code $1. @; if code='H' then input @3 vegetable $6.; if code='P'; input @3 Variety : $10. @15 Supplier : $15.;run;proc print data=perm.produce;run;

_N_	Vegetable	code	Variety	Supplier
6		P

_N_	Vegetable	code	Variety	Supplier
6	Squash	P

_N_	Vegetable	code	Variety	Supplier
6	Squash	H

_N_	Vegetable	code	Variety	Supplier
6	Squash	H	Yellow

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lee_jiayong

2016-8-4 13:22:06

因为程序里面有retain vegetable 这句话. 所以 vegetable这个变量在没有被改写之前还是保持着前一个iteration时的值. 题目中说第六次iteration只读到code, 也就是还没读到第六行的其他值, 因此vegetable这个变量依然保持着在第5次iteration 的值, 也就是squash. 因为其他变量还没读到,所以为缺失值.
第五次iteration不会出现B答案, 因为在第五次iteration的时候code 为 H