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发表于 2010-11-13 10:37:02
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跟crakman做sas base认证试题（53）
From crackman's blog on Baidu
<p><font size="4">53.The following SAS program is submitted:<br>
<br>
data WORK.TOTAL_SALARY;<br>
retain Total; <br>
set WORK.SALARY;<br>
by Department;<br>
if First.Department<br>
then Total=0;<br>
Total=sum(Total, Wagerate);<br>
if Last.Total;<br>
run;<br>
<br>
What is the initial value of the variable Total?</font></p>
<p><font size="4"> A. 0<br>
B. Missing<br>
C. The value of the first observations Wagerate<br>
D. Cannot be determined from the information given</font></p>
<p><font size="4">Answer: B </font></p>
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<p><font size="4">这里考察的是retain 语句。<br>
看看SAS HELP文档中对retain语句的解释：<br>
RETAIN <element-list(s) <initial-value(s) | <br>
(initial-value-1) | (initial-value-list-1) > <br>
< . . . element-list-n <initial-value-n | <br>
(initial-value-n ) | (initial-value-list-n)>>>; <br>
这里的retain total;<br>
只有total(element-list) 但是没有initial-value,如果忽略initial-value，那么就是默认为缺失值。<br>
If you omit initial-value, the initial value is missing</font></p> <a href="http://hi.baidu.com/crack%5Fman/blog/item/7bcab831bdb4d99ba71e1233.html">阅读全文</a>
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