sas的编译阶段

tailezhu2007

3566

收藏 2012-05-26

32.Consider the following data step:

data WORK.NEW;

set WORK.OLD;

Count+1;

run;

The variable Count is created using a sum statement. Which statement regarding this variable is true?

A. It is assigned a value 0 when the data step begins execution.

B. It is assigned a value of missing when the data step begins execution.

C. It is assigned a value 0 at compile time.

D. It is assigned a value of missing at compile time.

Answer: C

答案说在编译阶段就给赋值为0了。可是编译阶段不是都没有值吗？

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

tailezhu2007

2012-5-26 21:51:07

没人给说说吗？

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

bobguy

2012-5-26 22:40:48

First one needs to understand the retain statement. It is classified as non-executable statement. This is very important!

count +1;

is equivalent to

count=count+1;
retain count 0;

data t1;
set sashelp.class;
count=count+1;
retain count 0;
run;

proc print;run;

If you assign a missing to count in retain statement, you will get all counts as missing.

The other way to understand it is to wrap them into a do block as below,

if 0 then do;
set sashelp.class;
count+1;
end;

As we know that every statements will not get executed at running time because ' if 0  ' is never true. In other words these statements provide information at compiling time only.  The put statement let you see what is the value of count at compiling time .

data _null_;
  if 0 then do;
set sashelp.class;
count+1;
  end;
  put count;
run;

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

tailezhu2007

2012-5-26 23:43:13

bobguy 发表于 2012-5-26 22:40
First one needs to understand the retain statement. It is classified as non-executable statement. Th ...

Thank you very much.
就是英文能不能不这么给力啊！

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

tailezhu2007

2012-5-26 23:51:40