Logical (boolean) type in R Programming - Cheat Sheet & Quick Revision

Recall & Review

beginner

What values does the logical (boolean) type represent in R?

The logical type in R represents two main values: TRUE and FALSE. It is used to store truth values.

beginner

How do you create a logical vector with TRUE and FALSE values in R?

You can create a logical vector using the c() function, for example: c(TRUE, FALSE, TRUE).

beginner

What is the result of the expression 5 > 3 in R?

The expression 5 > 3 evaluates to TRUE because 5 is greater than 3.

intermediate

How does R treat the logical values TRUE and FALSE when used in arithmetic operations?

In arithmetic, TRUE is treated as 1 and FALSE as 0. For example, TRUE + TRUE equals 2.

intermediate

What function can you use to check if a value is logical in R?

You can use the is.logical() function to check if a value or vector is of logical type.

Which of the following is a logical value in R?

A 1

B "TRUE"

C 0

D TRUE

TRUE is a logical value. "TRUE" is a string, and 1 and 0 are numeric.

What does the expression is.logical(c(TRUE, FALSE, TRUE)) return?

A TRUE

B FALSE

C Error

D NULL

The vector contains logical values, so is.logical() returns TRUE.

What is the output of TRUE + FALSE in R?

A 0

B 1

C TRUE

D FALSE

TRUE is treated as 1 and FALSE as 0, so the sum is 1.

Which operator is used to compare two values and return a logical result?

A >

B +

C *

D -

The > operator compares values and returns TRUE or FALSE.

What is the class of the value FALSE in R?

A "numeric"

B "character"

C "logical"

D "integer"

FALSE is of class logical.

Explain what the logical (boolean) type is in R and give examples of how it is used.

Think about how R stores yes/no or true/false answers.

Describe how logical values behave when used in arithmetic operations in R.

Consider how R treats TRUE and FALSE as numbers.

Practice

1. What type of values does the logical type in R store?

easy

A. Numbers only

B. TRUE or FALSE

C. Text strings

D. Dates and times

Solution

1. Step 1: Understand logical type meaning

   Logical type in R is used to store values that represent truth values.

2. Step 2: Identify stored values

   These truth values are either TRUE or FALSE, not numbers, text, or dates.

3. Final Answer:

   TRUE or FALSE -> Option B

4. Quick Check:

   Logical type = TRUE or FALSE [OK]

Hint: Logical means true or false values only [OK]

Common Mistakes:

• Confusing logical with numeric type
• Thinking logical stores text
• Assuming logical stores dates

2. Which of the following is the correct way to create a logical vector in R?

easy

A. c('TRUE', 'FALSE')

B. c(1, 0, 1)

C. c(TRUE, FALSE, TRUE)

D. c(T, F, 'TRUE')

Solution

1. Step 1: Check vector creation syntax

   Logical vectors use TRUE or FALSE values without quotes inside c().

2. Step 2: Validate each option

   c(TRUE, FALSE, TRUE) uses proper logical values TRUE and FALSE. c('TRUE', 'FALSE') creates character vector. c(1, 0, 1) creates numeric vector. c(T, F, 'TRUE') mixes logical shortcuts T, F with string 'TRUE' coercing to character vector.

3. Final Answer:

   c(TRUE, FALSE, TRUE) -> Option C

4. Quick Check:

   Logical vector uses TRUE/FALSE without quotes [OK]

Hint: Use TRUE/FALSE without quotes for logical vectors [OK]

Common Mistakes:

• Using numbers instead of logical values
• Putting TRUE/FALSE in quotes
• Mixing logical and string types

3. What is the output of this R code?

result <- 5 > 3
print(result)

medium

A. TRUE

B. "TRUE"

C. FALSE

D. Error

Solution

1. Step 1: Evaluate the comparison 5 > 3

   Since 5 is greater than 3, the expression returns TRUE as a logical value.

2. Step 2: Understand print output

   print() outputs the logical value TRUE without quotes.

3. Final Answer:

   TRUE -> Option A

4. Quick Check:

   5 > 3 = TRUE [OK]

Hint: Comparison returns logical TRUE or FALSE, not strings [OK]

Common Mistakes:

• Thinking output is string "TRUE"
• Confusing TRUE with FALSE
• Expecting an error from comparison

4. Identify the error in this R code snippet:

flag <- TRUE
if flag == TRUE {
  print("Yes")
}

medium

A. Variable flag is not defined

B. Incorrect logical value TRUE

C. print() function is wrong

D. Missing parentheses around condition in if statement

Solution

1. Step 1: Check if statement syntax in R

   In R, the condition in if() must be inside parentheses.

2. Step 2: Identify missing parentheses

   The code uses if flag == TRUE without parentheses, causing syntax error.

3. Final Answer:

   Missing parentheses around condition in if statement -> Option D

4. Quick Check:

   if() needs parentheses [OK]

Hint: Always put condition inside parentheses in if() [OK]

Common Mistakes:

• Omitting parentheses in if condition
• Misusing TRUE value
• Assuming print() syntax is wrong

5. Given a numeric vector nums <- c(0, 1, 2, 3, 0), which R expression correctly creates a logical vector indicating which elements are non-zero?

hard

A. nums != 0

B. nums == TRUE

C. is.logical(nums)

D. nums > TRUE

Solution

1. Step 1: Understand the goal

   We want a logical vector showing TRUE where elements are not zero.

2. Step 2: Evaluate each option

   nums != 0 returns TRUE for non-zero elements. nums == TRUE compares to 1 (TRUE coerces to 1), TRUE only where nums==1. is.logical(nums) checks type of nums, returns single FALSE since it's numeric. nums > TRUE compares to 1, TRUE only where nums > 1.

3. Final Answer:

   nums != 0 -> Option A

4. Quick Check:

   nums != 0 gives logical TRUE for non-zero [OK]

Hint: Use != 0 to find non-zero elements logically [OK]

Common Mistakes:

• Using == TRUE to compare numbers
• Using is.logical() to check or create logical vector
• Comparing numbers directly to TRUE