SAS 编程中的 If-Then-Else 语句

使用条件语句时使用的比较运算符。

Symbol	Mnemonic	Meaning
=	EQ	equals
^= or ~=	NE	not equal
>	GT	greater than
<	LT	less than
>=	GE	greater than or equals
<=	LE	less than or equals
in	IN	selecting multiple values

1. IF 语句

   句法：

   IF (condition is true) => It means subsetting a dataset.

   例子：

   Data readin;
   Input R_Num Subj1-Subj3;
   cards;
   112 21 22 23
   105 23 24 26
   95 25 25 26
   125 26 26 24
   122 15 25 16
   86 26 16 15
   ;
     
   Data readin1;
   Set readin;
   IF R_Num GE 100;
   run; 
   

   输出：
   

   IF R_Num GE 100 => 这将告诉 SAS 仅保留值大于或等于 100 的卷号。换句话说，您正在删除值小于或等于 100 的卷号。

   也可以使用 IF-THEN DELETE 语句来完成。

2. 如果-则删除

   句法：

   IF (condition is true) THEN (delete the given statements);

   例子：

   Data readin;
   Input R_Num Subj1-Subj3;
   cards;
   112 21 22 23
   105 23 24 26
   95 25 25 26
   125 26 26 24
   122 15 25 16
   86 26 16 15
   ;
   Data readin1;
   Set readin;
   IF R_Num LT 100 THEN DELETE;
   run;
   

   输出：
   

   IF R_Num LT 100 THEN DELETE => 这将告诉 SAS 删除所有值小于 100 的卷号。

3. IF-THEN-ELSE 语句

   任务2：假设您要在所有R_Num 上设置一个标签。条件是：

   If the value of R_Num is less than 
   or equal to 100 sets "Old" tag 
   otherwise set "New" tag.

   IF (condition is true) THEN (perform this action);
   ELSE (perform the set of statements that is set when condition is false);

   Data readin;
   Input R_Num Subj1-Subj3;
   cards;
   112 21 22 23
   105 23 24 26
   95 25 25 26
   125 26 26 24
   122 15 25 16
   86 26 16 15
   ;
   Data readin1;
   Set readin;
   IF R_Num LE 100 THEN TAG ="Old";
   ELSE TAG ="New";
   run;
   

   输出：
   

4. IF-THEN-ELSE IF 语句

   任务 3：假设您被要求更新 TAG 列。

   标记条件如下：

   • 如果 R_Num 的值小于 75，则 TAG = “Old”
   • 如果 R_Num 的值大于或等于 75 且小于 100，则 TAG = “New”
   • 如果 R_Num 的值大于或等于 100，则 TAG = “未选中”

   IF (condition is true) THEN (perform this action);
   ELSE IF (perform the set of statements when second condition is true);
   ELSE IF (perform the set of statements when third condition is true);

   Data readin;
   Input R_Num Subj1-Subj3;
   cards;
   112 21 22 23
   105 23 24 26
   95 25 25 26
   125 26 26 24
   122 15 25 16
   86 26 16 15
   ;
   Data readin1;
   Set readin;
   length TAG $20;
   IF R_Num < 75 THEN TAG ="Old";
   ELSE IF 75 <= R_Num < 100 THEN TAG = "New"; 
   ELSE IF R_Num >= 100 THEN TAG ="Unchecked";
   run; 
   

   输出：