If...Else Ladder in R Programming Language: Syntax and Examples

if…else Ladder

The if…else ladder (if…else…if) statement allows you execute a block of code among more than 2 alternatives

The syntax of if…else statement is:

if ( test_expression1) {
statement1
} else if ( test_expression2) {
statement2
} else if ( test_expression3) {
statement3
} else {
statement4
}

Only one statement will get executed depending upon the test_expressions.

Example of nested if…else

x <- 0
if (x < 0) {
print("Negative number")
} else if (x > 0) {
print("Positive number")
} else
print("Zero")

Output

[1] "Zero" 

There is an easier way to use if…else statement specifically for vectors in R programming.

You can use ifelse() function instead; the vector equivalent form of the if…else statement.

Another Example of ifelse

Code

<span class="pln">
a </span><span class="pun">&lt;-</span><span class="pln"> c</span><span class="pun">(</span><span class="lit">1</span><span class="pun">,</span><span class="pln"> </span><span class="lit">1</span><span class="pun">,</span><span class="pln"> </span><span class="lit">0</span><span class="pun">,</span><span class="pln"> </span><span class="lit">1</span><span class="pun">)</span><span class="pln">
b </span><span class="pun">&lt;-</span><span class="pln"> c</span><span class="pun">(</span><span class="lit">2</span><span class="pun">,</span><span class="pln"> </span><span class="lit">1</span><span class="pun">,</span><span class="pln"> </span><span class="lit">0</span><span class="pun">,</span><span class="pln"> </span><span class="lit">1</span><span class="pun">)</span><span class="pln">

ifelse</span><span class="pun">(</span><span class="pln">a </span><span class="pun">==</span><span class="pln"> </span><span class="lit">1</span><span class="pln"> </span><span class="pun">&amp;</span><span class="pln"> b </span><span class="pun">==</span><span class="pln"> </span><span class="lit">1</span><span class="pun">,</span><span class="pln"> </span><span class="str">"Yes"</span><span class="pun">,</span><span class="pln"> </span><span class="str">"No"</span><span class="pun">)</span><span class="pln">

ifelse</span><span class="pun">(</span><span class="pln"> b </span><span class="pun">==</span><span class="pln"> </span><span class="lit">1</span><span class="pln"> </span><span class="pun">,</span><span class="pln">  </span><span class="str">"Hi"</span><span class="pun">,</span><span class="pln"> ifelse</span><span class="pun">(</span><span class="pln">b </span><span class="pun">==</span><span class="pln"> </span><span class="lit">0</span><span class="pun">,</span><span class="pln"> </span><span class="str">"Hello"</span><span class="pun">,</span><span class="pln"> </span><span class="str">"Goodbye"</span><span class="pun">))</span><span class="pln">

</span>

Output

<span class="pln">
</span><span class="pun">&gt;</span><span class="pln"> a </span><span class="pun">&lt;-</span><span class="pln"> c</span><span class="pun">(</span><span class="lit">1</span><span class="pun">,</span><span class="pln"> </span><span class="lit">1</span><span class="pun">,</span><span class="pln"> </span><span class="lit">0</span><span class="pun">,</span><span class="pln"> </span><span class="lit">1</span><span class="pun">)</span><span class="pln">
</span><span class="pun">&gt;</span><span class="pln"> b </span><span class="pun">&lt;-</span><span class="pln"> c</span><span class="pun">(</span><span class="lit">2</span><span class="pun">,</span><span class="pln"> </span><span class="lit">1</span><span class="pun">,</span><span class="pln"> </span><span class="lit">0</span><span class="pun">,</span><span class="pln"> </span><span class="lit">1</span><span class="pun">)</span><span class="pln">
</span><span class="pun">&gt;</span><span class="pln"> ifelse</span><span class="pun">(</span><span class="pln">a </span><span class="pun">==</span><span class="pln"> </span><span class="lit">1</span><span class="pln"> </span><span class="pun">&amp;</span><span class="pln"> b </span><span class="pun">==</span><span class="pln"> </span><span class="lit">1</span><span class="pun">,</span><span class="pln"> </span><span class="str">"Yes"</span><span class="pun">,</span><span class="pln"> </span><span class="str">"No"</span><span class="pun">)</span><span class="pln">
</span><span class="pun">[</span><span class="lit">1</span><span class="pun">]</span><span class="pln"> </span><span class="str">"No"</span><span class="pln">  </span><span class="str">"Yes"</span><span class="pln"> </span><span class="str">"No"</span><span class="pln">  </span><span class="str">"Yes"</span><span class="pln">
</span><span class="pun">&gt;</span><span class="pln"> ifelse</span><span class="pun">(</span><span class="pln"> b </span><span class="pun">==</span><span class="pln"> </span><span class="lit">1</span><span class="pln"> </span><span class="pun">,</span><span class="pln">  </span><span class="str">"Hi"</span><span class="pun">,</span><span class="pln"> ifelse</span><span class="pun">(</span><span class="pln">b </span><span class="pun">==</span><span class="pln"> </span><span class="lit">0</span><span class="pun">,</span><span class="pln"> </span><span class="str">"Hello"</span><span class="pun">,</span><span class="pln"> </span><span class="str">"Goodbye"</span><span class="pun">))</span><span class="pln">
</span><span class="pun">[</span><span class="lit">1</span><span class="pun">]</span><span class="pln"> </span><span class="str">"Goodbye"</span><span class="pln"> </span><span class="str">"Hi"</span><span class="pln">      </span><span class="str">"Hello"</span><span class="pln">   </span><span class="str">"Hi"</span><span class="pln">
</span>