Logical operators (&, |, !, &&, ||) in R Programming - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of vectorized logical AND (&) vs. element-wise AND (&&)

What is the output of the following R code snippet?

R Programming

x <- c(TRUE, FALSE, TRUE)
y <- c(FALSE, TRUE, TRUE)
result <- x & y
result2 <- x && y
print(result)
print(result2)

A

[1] FALSE FALSE TRUE
[1] FALSE

B

[1] TRUE TRUE TRUE
[1] TRUE

C

[1] FALSE TRUE FALSE
[1] TRUE

D

[1] TRUE FALSE TRUE
[1] FALSE

💡 Hint

Remember that & works element-wise on vectors, while && only checks the first element.

The & operator compares each element of x and y, producing a vector of logicals. The && operator only compares the first element of each vector, returning a single logical value.

❓ Predict Output

intermediate

Output of logical OR (|) with mixed TRUE and FALSE vectors

What will be printed by this R code?

R Programming

a <- c(FALSE, FALSE, TRUE)
b <- c(TRUE, FALSE, FALSE)
print(a | b)

A [1] FALSE TRUE TRUE

B [1] TRUE FALSE TRUE

C [1] TRUE TRUE TRUE

D [1] FALSE FALSE FALSE

💡 Hint

The | operator compares each element and returns TRUE if either is TRUE.

Element-wise OR returns TRUE if at least one element in the pair is TRUE. So positions: FALSE|TRUE=TRUE, FALSE|FALSE=FALSE, TRUE|FALSE=TRUE.

❓ Predict Output

advanced

Effect of ! (NOT) operator on a logical vector

What is the output of this R code?

R Programming

flags <- c(TRUE, FALSE, TRUE, FALSE)
negated <- !flags
print(negated)

A [1] FALSE TRUE FALSE TRUE

B [1] TRUE FALSE TRUE FALSE

C [1] FALSE FALSE FALSE FALSE

D [1] TRUE TRUE TRUE TRUE

💡 Hint

The ! operator flips TRUE to FALSE and FALSE to TRUE.

The NOT operator reverses each logical value in the vector.

❓ Predict Output

advanced

Difference between & and && in conditional statements

What will this R code print?

R Programming

x <- c(TRUE, FALSE)
if (x & TRUE) {
  print("A")
} else {
  print("B")
}
if (x && TRUE) {
  print("C")
} else {
  print("D")
}

A

B
C

B

B
D

C

A
C

D

A
D

💡 Hint

Remember that if expects a single TRUE or FALSE, && returns a single logical, & returns a vector.

The if with (x & TRUE) produces c(TRUE, FALSE), R warns and uses the first element TRUE, printing "A". The if with (x && TRUE) evaluates first elements TRUE && TRUE = TRUE, printing "C".

🧠 Conceptual

expert

Understanding short-circuit behavior of && and || in R

Which statement best describes the behavior of the && and || operators in R?

A && and || cannot be used in if statements because they return vectors.

B && and || are identical to & and | in all contexts.

C && and || evaluate all elements of logical vectors and return a vector of results.

D && and || evaluate only the first element of logical vectors and perform short-circuit evaluation.

💡 Hint

Think about how && and || behave differently from & and | when used in conditions.

In R, && and || only check the first element of logical vectors and stop evaluating further if the result is already determined (short-circuit). This makes them suitable for control flow statements like if.

Practice

1. Which logical operator in R checks every element of a vector and returns a vector of results?

easy

A. ==

B. & and |

C. !

D. && and ||

Solution

1. Step 1: Understand vectorized logical operators

   In R, & and | operate element-wise on vectors, returning a vector of TRUE/FALSE values for each element.

2. Step 2: Compare with single-element operators

   && and || only check the first element of the vectors and return a single TRUE/FALSE value.

3. Final Answer:

   & and | -> Option B

4. Quick Check:

   Element-wise operators = & and | [OK]

Hint: Use & and | for vectors, && and || for single values [OK]

Common Mistakes:

• Confusing && and & as the same
• Using || for vector comparisons
• Thinking ! works on multiple elements like &

2. Which of the following is the correct syntax to negate a logical vector v in R?

easy

A. !v

B. not(v)

C. ~v

D. v != TRUE

Solution

1. Step 1: Identify the negation operator in R

   The logical NOT operator in R is !, which negates each element of a logical vector.

2. Step 2: Check other options

   not() is not a base R function, ~ is a formula operator, and v != TRUE works but is less direct and less clear.

3. Final Answer:

   !v -> Option A

4. Quick Check:

   Negate vector with ! [OK]

Hint: Use ! to flip TRUE/FALSE values in R [OK]

Common Mistakes:

• Using not() which is not a base R function
• Confusing ~ with negation
• Using != TRUE instead of !

3. What is the output of the following R code?

v1 <- c(TRUE, FALSE, TRUE)
v2 <- c(FALSE, FALSE, TRUE)
v1 & v2
v1 && v2

medium

A. [1] TRUE TRUE TRUE
[1] TRUE

B. [1] TRUE FALSE TRUE
[1] TRUE

C. [1] FALSE FALSE FALSE
[1] FALSE

D. [1] FALSE FALSE TRUE
[1] FALSE

Solution

1. Step 1: Evaluate element-wise AND with &

   v1 & v2 compares each element:
   TRUE & FALSE = FALSE
   FALSE & FALSE = FALSE
   TRUE & TRUE = TRUE
   Result: [FALSE FALSE TRUE]

2. Step 2: Evaluate single-element AND with &&

   v1 && v2 checks only first elements:
   TRUE && FALSE = FALSE
   Result: [FALSE]

3. Final Answer:

   [1] FALSE FALSE TRUE [1] FALSE -> Option D

4. Quick Check:

   & compares all elements, && only first [OK]

Hint: & works element-wise; && checks first element only [OK]

Common Mistakes:

• Thinking && works element-wise
• Mixing up & and && results
• Ignoring vector length in &&

4. Identify the error in this R code snippet:

v <- c(TRUE, FALSE, TRUE)
if (v & TRUE) {
  print("Yes")
} else {
  print("No")
}

medium

A. Using & inside if condition causes error due to vector length

B. Missing parentheses around v & TRUE

C. Should use | instead of &

D. No error, code runs fine

Solution

1. Step 1: Understand if condition requirements

   The if statement expects a single TRUE or FALSE value, not a vector.

2. Step 2: Analyze v & TRUE

   v & TRUE returns a logical vector of length 3, which causes an error in if because it cannot handle multiple values.

3. Final Answer:

   Using & inside if condition causes error due to vector length -> Option A

4. Quick Check:

   if needs single TRUE/FALSE, & returns vector [OK]

Hint: Use && in if conditions for single TRUE/FALSE [OK]

Common Mistakes:

• Using & instead of && in if
• Assuming if accepts vector
• Ignoring error message about length

5. You have two logical vectors:

a <- c(TRUE, FALSE, TRUE, FALSE)
b <- c(FALSE, TRUE, TRUE, TRUE)

Write an expression using logical operators to find elements where either a is TRUE and b is FALSE, or a is FALSE and b is TRUE. What is the resulting vector?

hard

A. a | b resulting in [TRUE TRUE TRUE TRUE]

B. a & b resulting in [FALSE FALSE TRUE FALSE]

C. (a & !b) | (!a & b) resulting in [TRUE TRUE FALSE TRUE]

D. !(a | b) resulting in [FALSE FALSE FALSE FALSE]

Solution

1. Step 1: Understand the condition

   We want TRUE where exactly one of a or b is TRUE, but not both. This is the XOR condition.

2. Step 2: Write expression and evaluate

   (a & !b) | (!a & b) checks where a is TRUE and b is FALSE, or vice versa.
   Evaluate:
   a: TRUE FALSE TRUE FALSE
   b: FALSE TRUE TRUE TRUE
   a & !b: TRUE FALSE FALSE FALSE
   !a & b: FALSE TRUE FALSE TRUE
   OR: TRUE TRUE FALSE TRUE

3. Final Answer:

   (a & !b) | (!a & b) resulting in [TRUE TRUE FALSE TRUE] -> Option C

4. Quick Check:

   XOR = (a & !b) | (!a & b) [OK]

Hint: Use (a & !b) | (!a & b) for XOR logic [OK]

Common Mistakes:

• Using & or | alone instead of XOR logic
• Forgetting to negate one vector
• Confusing XOR with OR