Conditional statements allow R programs to execute different blocks of code based on certain conditions.

Basic Syntax

if (condition) {
  # code to execute if condition is True
}

Example

x <- 10
if (x > 5) {
  print("x is greater than 5")
}

## [1] "x is greater than 5"

• Executes the print statement because the condition (x > 5) is True.

Extending if with else

if (condition) {
  # code if condition is True
} else {
  # code if condition is False
}

Example

x <- 3
if (x > 5) {
  print("x is greater than 5")
} else {
  print("x is not greater than 5")
}

## [1] "x is not greater than 5"

• Executes the second print statement because the condition is False.

For Multiple Conditions

if (condition1) {
  # code if condition1 is True
} else if (condition2) {
  # code if condition2 is True
} else {
  # code if neither condition is True
}

Example

x <- 5
if (x > 5) {
  print("x is greater than 5")
} else if (x == 5) {
  print("x is equal to 5")
} else {
  print("x is less than 5")
}

## [1] "x is equal to 5"

• Executes the print statement in the else if block.

The any function is a logical operation in R that tests if any of the elements in a given vector or data structure are TRUE.

Example

values <- c(TRUE, FALSE, FALSE)
result <- any(values)
print(result) # Output: TRUE

## [1] TRUE

The all function is a logical operation in R that tests if all of the elements in a given vector or data structure are TRUE.

Example

values <- c(TRUE, FALSE, FALSE)
result <- all(values)
print(result) # Output: FALSE

## [1] FALSE

ifelse(test_expression, yes, no)

• The ifelse function is a vectorized conditional function which evaluates each element of the test_expression.

• If the condition for an element is TRUE, it returns the corresponding element from yes; otherwise, it returns the corresponding element from no.

Example

x <- 5
result <- ifelse(x > 10, "Greater than 10", "Less or equal to 10")
print(result)

## [1] "Less or equal to 10"

• Returns a character vector: "Less or equal to 10".

Example

x <- c(5, 10, 15)
result <- ifelse(x > 10, "Greater than 10", "Less or equal to 10")
print(result)

## [1] "Less or equal to 10" "Less or equal to 10" "Greater than 10"

• Returns a character vector: ["Less or equal to 10", "Less or equal to 10", "Greater than 10"].

• Type Coercion: The yes and no arguments must be the same type, or they will be coerced to a common type, which might not be intended.

x <- c(5, 10, 15)
result <- ifelse(x > 10, x, "Less or equal to 10")
print(result)

## [1] "Less or equal to 10" "Less or equal to 10" "15"

• Returns a character vector: ["Less or equal to 10", "Less or equal to 10", "15"].

• Last element is coerced to character.

Loops in R are used to execute a block of code repeatedly.

Iterating Over Sequences

for (element in sequence) {
  # code to execute for each element
}

Example

fruits <- c("apple", "banana", "cherry")
for (fruit in fruits) {
  print(fruit)
}

## [1] "apple"
## [1] "banana"
## [1] "cherry"

• Prints each fruit in the vector.

Example

# Print numbers 1 through 5
for(i in 1:5) {
  print(i)
}

## [1] 1
## [1] 2
## [1] 3
## [1] 4
## [1] 5

• Prints the numbers 1 through 5.

Repeating While a Condition is True

while (condition) {
  # code to execute while condition is True
}

Example

# Print numbers 1 through 5
i <- 1
while(i <= 5) {
  print(i)
  i <- i + 1
}

## [1] 1
## [1] 2
## [1] 3
## [1] 4
## [1] 5

• Continues to execute as long as the condition is TRUE.

What does the following code print?

if (FALSE) {
  print("False!")
} else if (TRUE) {
  print("Now True!")
} else {
  print("Finally True!")
}

## [1] "Now True!"

1. False!
2. Now True!
3. Finally True!
4. Nothing

How many times does the following loop run?

x <- 3
while (x < 8) {
  print("Looping!")
  x <- x + 2
}

## [1] "Looping!"
## [1] "Looping!"
## [1] "Looping!"

1. 2 times
2. 3 times
3. 4 times
4. 5 times

Consider the following code:

numbers <- c(1, 4, 7, 10) # Initial vector of numbers
target <- 5               # Target value
i <- 1                    # Index to traverse the vector

while(any(numbers != target)) {

  i <- ifelse(numbers[i]==target, i + 1, i)

  numbers[i] <- ifelse(numbers[i] < target, 
                       numbers[i] + 1, 
                       numbers[i] - 1)

  print(numbers)
}

What will be the final state of the numbers vector after the loop terminates?

1. c(5, 5, 5, 5)
2. c(2, 5, 8, 11)
3. The loop will not terminate and result in an infinite loop.
4. c(1, 4, 7, 10)

What will the following code output?

for(i in c(1, 3, 5)) {
  if(i %% 2 == 0) {
    print("Even")
  } else {
    print("Odd")
  }
}

1. Even Odd Even
2. Odd Odd Odd
3. Even Even Even
4. Odd Even Odd

What will the following code output?

for(i in c(1, 3, 5)) {
  if(i %% 2 == 0) {
    print("Even")
  } else {
    print("Odd")
  }
}