跟crakman做sas base认证试题（2）-经管之家官网！

2.Given the following raw data records in TEXTFILE.TXT:
----|----10---|----20---|----30
John,FEB,13,25,14,27,Final
John,MAR,26,17,29,11,23,Current
Tina,FEB,15,18,12,13,Final
Tina,MAR,29,14,19,27,20,Current
The following output is desired:
Obs Name Month Status Week1 Week2 Week3 Week4 Week5
1 John FEB Final $13 $25 $14 $27 .
2 John MAR Current $26 $17 $29 $11 $23
3 Tina FEB Final $15 $18 $12 $13 .
4 Tina MAR Current $29 $14 $19 $27 $20
Which SAS program correctly produces the desired output?
A.
data WORK.NUMBERS;
length Name $ 4 Month $ 3 Status $ 7;
infile 'TEXTFILE.TXT' dsd;
input Name $ Month $;
if Month='FEB' then input Week1 Week2 Week3 Week4 Status $;
else if Month='MAR' then input Week1 Week2 Week3 Week4 Week5 Status $;
format Week1-Week5 dollar6.;
run;
proc print data=WORK.NUMBERS;
run;
B.
data WORK.NUMBERS;
length Name $ 4 Month $ 3 Status $ 7;
infile 'TEXTFILE.TXT' dlm=',' missover;
input Name $ Month $;
if Month='FEB' then input Week1 Week2 Week3 Week4 Status $;
else if Month='MAR' then input Week1 Week2 Week3 Week4 Week5 Status $;
format Week1-Week5 dollar6.;
run;
proc print data=WORK.NUMBERS;
run;
C.
data WORK.NUMBERS;
length Name $ 4 Month $ 3 Status $ 7;
infile 'TEXTFILE.TXT' dlm=',';
input Name $ Month $ @;
if Month='FEB' then input Week1 Week2 Week3 Week4 Status $;
else if Month='MAR' then input Week1 Week2 Week3 Week4 Week5 Status $;
format Week1-Week5 dollar6.;
run;
proc print data=WORK.NUMBERS;
run;
D.
data WORK.NUMBERS;
length Name $ 4 Month $ 3 Status $ 7;
infile 'TEXTFILE.TXT' dsd @;
input Name $ Month $;
if Month='FEB' then input Week1 Week2 Week3 Week4 Status $;
else if Month='MAR' then input Week1 Week2 Week3 Week4 Week5 Status $;
format Week1-Week5 dollar6.;
run;
proc print data=WORK.NUMBERS;
run;
Answer: C
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这道题其实考察的是读入外部文本数据时几个知识点，1.INFILE语句读入外部数据时候，参数MISSOVER以及DSD DLM的参数意义；2.INPUT读入数据的指针；3.@符号对指针的影响。
下面逐个对着程序，来解剖一下执行过程。
A.DSD：规定若一个数据是由引号，那么SAS认为引号内的逗号也是属于字符数据；设定默认分隔符为逗号；连续两个分隔符之间的数据位缺失值；读入数据时去掉引号。
input语句在读入观测时，先从第一行“John,FEB,13,25,14,27,Final”读取数据“John,FEB”就转入到了第二行“John,MAR,26,17,29,11,23,Current”，那么因为month="FEB"是true
所以接着在第二行“John,MAR,26,17,29,11,23,Current”，读入week1 week2，但是john mar都是字符型，而week1 week2默认为数值型，所以就是缺失值。继续读入week3 week4也就是26 17
接着就是status 是29。读完之后回到infile，回到input,从第三行开始读"Tina,FEB,15,18,12,13,Final",读入name month之后，转达到第四行“Tina,MAR,29,14,19,27,20,Current”。
B.MISSOVER：组织INPUT从下一个数据行中读入数据，未赋值的变量就是缺失值。
其实从A看出，因为第一次INPUT只读入第一数据行两个值，指针转入到第二行了。那么MISSOVER是否可以阻止呢？肯定不能阻止，因为INPUT第一次就只读入两个数据，而且第一行的数据也是
大于2个的，所以根本就无需阻止。自己读完两个数据之后自动转向第二行。不能让第一次和第二次的input指针保留在同一行中。
C.正确答案。原因很简单，因为@符号，让第一个INPUT读完数据之后，指针依然留在第一个数据行，等待第二个INPUT来读入后续的数据。
D.不用解释。INFILE后面加一个@本身就是错误，编译错误