Decision-Making Statements in R

Introduction

Decision-making statements are control structures that enable a program to choose different courses of action based on specified conditions. They allow the program to make decisions and execute different blocks of code depending on whether a condition evaluates to TRUE or FALSE.

In R, decision-making statements are used to:

• Test conditions.
• Execute specific statements when conditions are satisfied.
• Select one block of code among several alternatives.
• Implement logical decisions in programs.

The major decision-making constructs in R are:

1. if Statement
2. if-else Statement
3. if-else-if Ladder
4. Nested if Statement
5. switch() Statement
6. ifelse() Function

---

1. if Statement

Definition

The if statement executes a block of code only when a specified condition is TRUE.

Syntax

if(condition)
{
    statements
}

Flowchart

          Condition
               |
          +----+----+
          |         |
        TRUE      FALSE
          |         |
     Execute       Skip
     statements

Example

marks <- 80

if(marks >= 50)
{
    print("Pass")
}

Output

[1] "Pass"

Applications

• Positive/negative number check
• Even/odd number check
• Eligibility verification

---

2. if-else Statement

Definition

The if-else statement provides two alternative execution paths. One block is executed when the condition is TRUE, and another block is executed when the condition is FALSE.

Syntax

if(condition)
{
    statements1
}
else
{
    statements2
}

Flowchart

           Condition
               |
         +-----+-----+
         |           |
       TRUE        FALSE
         |           |
   Execute if     Execute else
      block          block

Example

num <- 7

if(num %% 2 == 0)
{
    print("Even Number")
}
else
{
    print("Odd Number")
}

Output

[1] "Odd Number"

Applications

• Pass/Fail determination
• Even/Odd checking
• Voting eligibility

---

3. if-else-if Ladder

Definition

The if-else-if ladder is used when multiple conditions need to be tested. The conditions are checked sequentially until one of them becomes TRUE.

Syntax

if(condition1)
{
    statements1
}
else if(condition2)
{
    statements2
}
else if(condition3)
{
    statements3
}
else
{
    statements4
}

Example

marks <- 82

if(marks >= 90)
{
    grade <- "A"
}
else if(marks >= 75)
{
    grade <- "B"
}
else if(marks >= 60)
{
    grade <- "C"
}
else
{
    grade <- "F"
}

print(grade)

Output

[1] "B"

Applications

• Grade calculation
• Salary classification
• Menu selection

---

4. Nested if Statement

Definition

An if statement inside another if statement is called a nested if statement.

Syntax

if(condition1)
{
    if(condition2)
    {
        statements
    }
}

Example

age <- 20
citizen <- TRUE

if(age >= 18)
{
    if(citizen)
    {
        print("Eligible to vote")
    }
}

Output

[1] "Eligible to vote"

Applications

• Multi-level decision making
• Admission eligibility
• Authentication systems

---

5. switch() Statement

Definition

The switch() function selects one option from multiple alternatives. It behaves similarly to the switch-case statement found in other programming languages.

Syntax

switch(expression,
       case1,
       case2,
       ...)

Example 1: Numeric Expression

choice <- 2

fruit <- switch(choice,
                "Apple",
                "Orange",
                "Mango")

print(fruit)

Output

[1] "Orange"

---

Example 2: Character Expression

operation <- "add"

result <- switch(operation,
                 add = 10 + 20,
                 sub = 10 - 20,
                 mul = 10 * 20)

print(result)

Output

[1] 30

Applications

• Menu-driven programs
• Calculator programs
• Multiple-choice selection

---

6. ifelse() Function

Definition

The ifelse() function performs vectorized conditional operations. It returns one value when the condition is TRUE and another when it is FALSE.

Syntax

ifelse(condition,
       value_if_true,
       value_if_false)

Example

marks <- c(80, 40, 90, 30)

result <- ifelse(marks >= 50,
                 "Pass",
                 "Fail")

print(result)

Output

[1] "Pass" "Fail" "Pass" "Fail"

Applications

• Assigning grades
• Creating new columns in data frames
• Vectorized computations

---

Comparison of Decision-Making Statements

Statement	Number of Conditions	Number of Alternatives
if	One	One
if-else	One	Two
if-else-if	Multiple	Multiple
Nested if	Multiple (hierarchical)	Multiple
switch()	Multiple choices	One selected choice
ifelse()	Vectorized condition	Two

---

Example Program

marks <- 78

if(marks >= 90)
{
    grade <- "A"
}
else if(marks >= 75)
{
    grade <- "B"
}
else if(marks >= 60)
{
    grade <- "C"
}
else
{
    grade <- "F"
}

print(paste("Grade =", grade))

Output

[1] "Grade = B"

---

Summary

Construct	Purpose
if	Execute statements when condition is TRUE
if-else	Select between two alternatives
if-else-if	Select among multiple alternatives
Nested if	Hierarchical decision making
switch()	Choose one option from many
ifelse()	Vectorized conditional evaluation

---

Conclusion

Decision-making statements are fundamental control structures in R that allow programs to respond differently to different situations. The if, if-else, and if-else-if constructs provide conditional execution, while nested if statements handle complex decisions. The switch() statement is useful for menu-driven applications, and the ifelse() function supports efficient vectorized conditional operations. These constructs are essential for developing logical, interactive, and intelligent programs in R and form the basis for more advanced programming techniques.