SAS : IF-Then-Else Statements

Task 1 : Suppose you are asked to exclude some of the observations in a SAS data set from an analysis that you are generating. For example, you want to exclude all IDs whose values are greater than 100.

To accomplish this task, we can use IF, IF-THEN DELETE.

Comparison Operators

Symbolic
Mnemonic
Meaning
Example
=
EQ
equals
IF gender = ‘M’; or

IF gender EQ ‘M’;
^= or ~=
NE
not equal
IF salary NE . ;
> 
GT
greater than
IF salary GT 4500;
< 
LT
less than
IF salary LT 4500;
>=
GE
greater than or equal
IF salary GE 4500;
<=
LE
less than or equal
IF salary LE 4500;
in
IN
selecting multiple values
IF country IN(‘US’ ’IN’);


1. IF statement

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



The output is shown below :



IF ID LE 100 => This would tell SAS to retain only those IDs whose values are less than or equal to 100. In other words, you are removing IDs whose values are greater than or equal to 100.

This can also be done using the IF-THEN DELETE statement.


2. IF-THEN DELETE

IF (condition is true) THEN (delete the selected observations);



IF ID GT 100 THEN DELETE => This would tell SAS to remove all the IDs whose values are greater than 100.





II. IF-THEN-ELSE Statement

Task 2: Suppose you want to set a tag on all the IDs. The condition is :

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

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



Syntax of IF-THEN-ELSE :


The output is shown below :




III. IF-THEN-ELSE IF Statement

Task 3: Suppose you are asked to update the TAG column.

The conditions for tagging are as follows :
  • If value of ID is less than 75 then TAG = "Old"
  • If value of ID is greater than or equal to 75 and less than 100 then TAG = "New"
  • If value of ID is greater than or equal to 100 then TAG = "Unchecked"
IF (condition is true) THEN (perform this action);
ELSE IF (perform the action when second condition is true);
ELSE IF (perform the action when third condition is true);



Syntax of IF-THEN-ELSE IF : 



The output is shown below :




LOGICAL OPERATORS


Symbolic
Mnemonic
Meaning
Example
&
AND
Both conditions true
IF gender =’M’ and age =1;
|
OR
Either condition true
IF gender =’M’ or age =1;
~ or ^
NOT
Reverse the statement
IF country not IN(‘US’,’IN’);

Task 4: Suppose you want to generate an analysis for Q1 including only responses that are valid (non-missing) and less than 3.



IF (Q1 LT 3) AND (Q1 NE .) => Since missing values are smaller than any other value, we need to give SAS an additional command to separate out missing values. 

The output is shown below:



Selecting Multiple Observations :

Suppose you want to set tag "Incorrect" to the specified IDs 1,5,45,76

For this case, the logical statement would look like any one of the following statements. It can be written in three ways shown below.


IN Operator

IN operator is used to select multiple values of a variable. It is an awesome alternative to OR operator.



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2 Responses to "SAS : IF-Then-Else Statements"

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  2. Please can you explain us details about if/then/else.How behind the scene it works. I try to get the clue but still I am not clear.For example putting if only without else how it works ? putting else if how it works ? At end only else how it works ? Putting only if without then how it works? How it works with do loop and array ? Basically while I am trying to understand Sas certified question (Mostly program with if/then/else/do statement and question is how many observations)it making me a lot confuse.

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