SAS BASE 67题请教

lapommier

6245

收藏 2013-02-20

Q 67

Consider the following data step:

data WORK.NEW;

set WORK.OLD(keep=X);

if X < 10 then X=1;

else if X >= 10 AND X LT 20 then X=2;

else X=3;

run;

In filtering the values of the variable X in data set WORK.OLD, what value new value would be assigned to X if its original value was a missing value?

A. X would get a value of 1.

B. X would get a value of 3.

C. X would retain its original value of missing.

D. This step does not run because of syntax errors.

答案：A

为什么X的值是1?

扫码加我拉你入群

请注明：姓名-公司-职位

以便审核进群资格，未注明则拒绝

全部回复

pobel

2013-2-20 12:01:15

SAS中缺失值是小于任何一个值的。
此题中，如果x是缺失值，那么x<10 成立，因此选A。

不过缺失值有多种表示方法，如., ._, .A, .B, 等等。而且这些缺失值是有大小顺序的。
如果用missing（）函数判断，那么这些值都是缺失的。
如果用“if x=. then ...”判断，则只有 . 这个值是满足条件的。

data test;
verysmall=-9999999;
miss_dot=.;
miss_a=.A;
miss_n=.N;
miss_z=.Z;
miss__=._;

if miss__ < miss_dot then put "._ < .";
if miss_dot < miss_a then put ". < .A";
if miss_a < miss_n then put ".A < .N";
if miss_n < miss_z then put ".N < .Z";
if miss_z < verysmall then put ".Z < verysmall";
run;