R Decision Making or Conditional Statements

R Decision Making

In R programming, Decision Making statements help to decide whether to execute a block of code or not, based on a condition. Decision making is an important aspect in any programming language. Decision Making statements are also called Conditional statement.

In this tutorial, we list out decision making statements available in R language, and go through examples for each of them.

R conditional statements are used when a program has to choose between different paths. For example, an R script may print a message only when a value crosses a threshold, classify a score into a grade, or select one result from a group of options.

The following are detailed tutorials for each of the decision making statements in R.

• R if statement
• R if-else statement
• R if-else-if statement
• R switch statement

What is a decision making statement in R?

A decision making statement in R is a control structure that evaluates a condition and then decides which statement or block should run. The condition must evaluate to a logical value, usually TRUE or FALSE.

For scalar decisions, R commonly uses if, if...else, if...else if...else, and switch(). For vectorized decisions, R also provides functions such as ifelse(), but ifelse() is different from the regular control-flow if statement.

R conditional statements at a glance

R decision making statement	When to use it	Example use case
if	Run a block only when one condition is TRUE.	Print a warning when a value is negative.
if...else	Choose between two possible branches.	Print pass or fail based on marks.
if...else if...else	Choose one branch from many conditions.	Classify marks into grades.
switch()	Select a value or expression based on an index or name.	Return a label for a selected option.

The examples below show each R decision making statement in a simple form. The condition examples use == for equality comparison, not assignment.

R If Statement

In If statement, a condition (boolean expression) is evaluated. If the result is TRUE, then a block of statements are executed.

The basic syntax of an R if statement is shown below.

if (condition) {
  # statements to run when condition is TRUE
}

Example.R

a <- 6

if (a == 6) {
  print("a is 6.")
}

print("End of program.")

Output

[1] "a is 6."
[1] "End of program."

If the condition evaluates to FALSE, then if-block is not executed, and the execution continues with the statements after If statement.

Example.R

a <- 10

if (a == 6) {
  print("a is 6.")
}

print("End of program.")

Output

[1] "End of program."

Here, a == 6 is FALSE, so the block inside if is skipped. The final print statement runs because it is outside the if block.

R If-Else Statement

A boolean expression is evaluated and if TRUE, statements in if-block are execute, otherwise else-block statements are executed.

The else block gives one alternate path when the if condition is not satisfied.

if (condition) {
  # statements when condition is TRUE
} else {
  # statements when condition is FALSE
}

Example.R

a <- 10

if (a == 6) {
  print("a is 6.")
} else {
  print("a is not 6.")
}

print("End of program.")

Output

[1] "a is not 6."
[1] "End of program."

Since a == 6 is FALSE, R runs the else block and then continues with the statements after the complete if...else structure.

R If-Else-If Statement

This is kind of a chained if-else statement. From top to down, whenever a condition evaluates to TRUE, corresponding block is executed, and the control exits from this if-else-if statement.

Use an R if...else if...else ladder when there are more than two possible outcomes. R checks conditions in order and executes only the first matching branch.

if (condition_1) {
  # statements when condition_1 is TRUE
} else if (condition_2) {
  # statements when condition_2 is TRUE
} else {
  # statements when no earlier condition is TRUE
}

Example.R

a <- 10

if (a == 6) {
  print("a is 6.")
} else if (a == 10) {
  print("a is 10.")
} else if (a == 20) {
  print("a is 20.")
}

print("End of program.")

Output

[1] "a is 10."
[1] "End of program."

In this example, the first condition is false and the second condition is true. Therefore, R prints "a is 10.". The later else if condition is not evaluated after the match is found.

R if else if ladder for grade classification

The order of conditions is important in an R if...else if ladder. For range-based decisions, place the highest or most specific condition first.

marks <- 82

if (marks >= 90) {
  grade <- "A"
} else if (marks >= 75) {
  grade <- "B"
} else if (marks >= 60) {
  grade <- "C"
} else if (marks >= 40) {
  grade <- "D"
} else {
  grade <- "Fail"
}

print(grade)

Output

[1] "B"

Although marks >= 60 is also true for 82, R stops at the first true condition, marks >= 75.

R Switch Statement

In R Switch statement, an expression is evaluated and based on the result, a value is selected from a list of values.

The switch() function is useful when the program must select one value from a fixed set of choices. The selection can be based on a number or a name.

result <- switch(expression, option_1, option_2, option_3)

Example.R

y <- 3

x <- switch(
  y,
  "Good Morning",
  "Good Afternoon",
  "Good Evening",
  "Good Night"
)

print(x)

Output

[1] "Good Evening"

Here, y is 3, so switch() selects the third value from the list and assigns it to x.

R switch statement with named choices

A named switch() statement can be easier to read when choices are labels such as "add", "subtract", or "divide".

operation <- "multiply"
a <- 4
b <- 5

answer <- switch(
  operation,
  add = a + b,
  subtract = a - b,
  multiply = a * b,
  divide = a / b
)

print(answer)

Output

[1] 20

Since operation is "multiply", R evaluates the named expression multiply = a * b.

Multiple conditions in R decision making statements

R conditions can combine more than one comparison. Use && when both scalar conditions must be true. Use || when at least one scalar condition must be true.

age <- 21
has_id <- TRUE

if (age >= 18 && has_id == TRUE) {
  print("Allowed")
} else {
  print("Not allowed")
}

Output

[1] "Allowed"

For scalar decision making with if, && and || are usually clearer than the vectorized operators & and |. Use vectorized operators when you intentionally compare vectors element by element.

Comparison operators used in R conditional statements

Most R conditional statements use comparison operators inside the condition. These operators return logical values such as TRUE or FALSE.

Operator	Meaning in an R condition	Example
==	Equal to	a == 10
!=	Not equal to	a != 10
>	Greater than	a > 10
>=	Greater than or equal to	a >= 10
<	Less than	a < 10
<=	Less than or equal to	a <= 10

A common mistake is to use assignment when a comparison is needed. Inside a condition, use == to test equality.

R if statements and vectorized ifelse()

The regular R if statement is meant for one logical decision. When you need to apply a condition across every element in a vector, use ifelse().

scores <- c(35, 60, 78, 92)
result <- ifelse(scores >= 40, "Pass", "Fail")

print(result)

Output

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

Use if...else for control flow and use ifelse() for element-by-element conditional results in vectors.

Common mistakes in R decision making statements

• Using elif in R: R uses else if, not elif.
• Using = instead of == in a condition: Use == when you want to compare two values.
• Writing broad range checks first: In an if...else if ladder, the first true condition wins.
• Passing a vector condition to if: Use a single logical value for if. Use ifelse() for vectors.
• Putting else on a detached line: Keep else with the closing brace of the previous block, as in } else {.

QA checklist for R conditional statements examples

• Confirm that each R if condition evaluates to one logical result for scalar control flow.
• Check that every else if condition is written after else and before its code block.
• Verify that switch() examples use the correct numeric position or named choice.
• Run each R example and compare the actual console output with the output shown in the tutorial.
• Check that range-based examples place the most restrictive or highest-priority condition first.

FAQs on R decision making and conditional statements

Conclusion on R decision making statements

In this R tutorial, we learned about R decision making / conditional statements – If, If-Else, If-Else-If, and Switch. Use if for a single condition, if...else for two branches, if...else if...else for multiple ordered conditions, and switch() when you need to select from fixed choices.