Type checking and conversion in R Programming - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of type conversion with as.numeric()

What is the output of the following R code?

R Programming

x <- c("10", "20", "thirty", "40")
y <- as.numeric(x)
y

A [1] 10 20 NA 40

B [1] "10" "20" "thirty" "40"

C [1] 10 20 30 40

D [1] NA NA NA NA

💡 Hint

as.numeric() converts strings to numbers but returns NA for non-numeric strings.

The string "thirty" cannot be converted to a number, so as.numeric() returns NA for that element.

❓ Predict Output

intermediate

Result of is.integer() on numeric vector

What does the following R code print?

R Programming

v <- c(1, 2, 3)
is.integer(v)

A [1] TRUE

B [1] NA

C [1] FALSE

D Error: object 'v' not found

💡 Hint

In R, numeric vectors are by default of type double, not integer.

The vector v is numeric (double), so is.integer(v) returns FALSE.

❓ Predict Output

advanced

Behavior of as.character() on factor

What is the output of this R code?

R Programming

f <- factor(c("apple", "banana", "apple"))
char_vec <- as.character(f)
char_vec

A [1] "apple" "banana" "apple"

B [1] 1 2 1

C [1] "1" "2" "1"

D [1] NA NA NA

💡 Hint

as.character() converts factor levels back to their string values.

Factors store data as integers internally but as.character() returns the original strings.

❓ Predict Output

advanced

Output of typeof() on logical conversion

What is the output of this R code?

R Programming

x <- c(TRUE, FALSE, TRUE)
t <- as.integer(x)
t
typeof(t)

A

[1] 1 0 1
[1] "double"

B

[1] 1 0 1
[1] "integer"

C

[1] TRUE FALSE TRUE
[1] "logical"

D

[1] NA NA NA
[1] "integer"

💡 Hint

TRUE converts to 1 and FALSE to 0 when cast to integer.

as.integer converts logical TRUE/FALSE to 1/0 and typeof confirms the vector type is integer.

❓ Predict Output

expert

Result of coercion in mixed-type vector

What is the output of this R code?

R Programming

v <- c(1L, 2.5, TRUE, "4")
v
typeof(v)

A

[1] 1 2.5 1 NA
[1] "double"

B

[1] 1 2 1 4
[1] "integer"

C

[1] 1 2.5 1 4
[1] "double"

D

[1] "1" "2.5" "TRUE" "4"
[1] "character"

💡 Hint

When combining different types, R coerces all elements to the most flexible type.

Because of the character "4", all elements become character strings.

Practice

1. Which function in R checks if a variable is of numeric type?

easy

A. as.character()

B. as.numeric()

C. is.character()

D. is.numeric()

Solution

1. Step 1: Understand type checking functions

   Functions starting with is. check the type of a variable.

2. Step 2: Identify the correct function for numeric check

   is.numeric() returns TRUE if the variable is numeric.

3. Final Answer:

   is.numeric() -> Option D

4. Quick Check:

   Type check numeric = is.numeric() [OK]

Hint: Use is.type() to check type, as.type() to convert [OK]

Common Mistakes:

• Confusing is.numeric() with as.numeric()
• Using as.character() to check type
• Using is.character() for numeric check

2. Which of the following is the correct way to convert a character vector c("1", "2", "3") to numeric in R?

easy

A. is.numeric(c("1", "2", "3"))

B. as.numeric(c("1", "2", "3"))

C. as.character(c(1, 2, 3))

D. is.character(c(1, 2, 3))

Solution

1. Step 1: Identify conversion functions

   as.numeric() converts data to numeric type.

2. Step 2: Apply conversion to character vector

   Using as.numeric(c("1", "2", "3")) converts strings to numbers 1, 2, 3.

3. Final Answer:

   as.numeric(c("1", "2", "3")) -> Option B

4. Quick Check:

   Convert char to numeric = as.numeric() [OK]

Hint: Use as.numeric() to convert strings to numbers [OK]

Common Mistakes:

• Using is.numeric() instead of as.numeric()
• Trying to convert numeric to character for numeric conversion
• Confusing is.character() with conversion functions

3. What will be the output of the following R code?

vec <- c("10", "20", "30")
num_vec <- as.numeric(vec)
is.numeric(num_vec)

medium

A. TRUE

B. FALSE

C. Error

D. NA

Solution

1. Step 1: Convert character vector to numeric

   as.numeric(vec) changes strings "10", "20", "30" to numbers 10, 20, 30.

2. Step 2: Check if converted vector is numeric

   is.numeric(num_vec) returns TRUE because num_vec is numeric.

3. Final Answer:

   TRUE -> Option A

4. Quick Check:

   as.numeric() converts, is.numeric() confirms [OK]

Hint: as.numeric() converts, is.numeric() checks type [OK]

Common Mistakes:

• Expecting FALSE because original was character
• Thinking as.numeric() returns character
• Confusing is.numeric() with as.numeric()

4. Identify the error in the following R code snippet:

val <- "123abc"
num_val <- as.numeric(val)
print(num_val)

medium

A. No error, prints 123

B. Syntax error due to quotes

C. Prints NA with a warning

D. Prints 0 without warning

Solution

1. Step 1: Attempt to convert mixed string to numeric

   as.numeric("123abc") cannot convert because of non-numeric characters.

2. Step 2: Result of conversion

   It returns NA and shows a warning about NAs introduced by coercion.

3. Final Answer:

   Prints NA with a warning -> Option C

4. Quick Check:

   Invalid numeric conversion = NA + warning [OK]

Hint: Invalid numeric strings convert to NA with warning [OK]

Common Mistakes:

• Expecting partial numeric conversion
• Ignoring warning messages
• Assuming syntax error due to quotes

5. You have a list lst <- list("5", 10, "abc", "15.5"). Which R code correctly converts all elements to numeric, replacing non-convertible values with 0?

hard

A. sapply(lst, function(x) if(is.na(as.numeric(x))) 0 else as.numeric(x))

B. sapply(lst, function(x) as.numeric(x))

C. sapply(lst, function(x) if(is.na(as.numeric(x))) as.numeric(x) else 0)

D. sapply(lst, function(x) if(is.numeric(x)) x else 0)

Solution

1. Step 1: Convert each element to numeric and check for NA

   Use as.numeric(x) inside a function and check if result is NA.

2. Step 2: Replace NA with 0, else keep numeric value

   If as.numeric(x) is NA, return 0; otherwise return the numeric value.

3. Final Answer:

   sapply(lst, function(x) if(is.na(as.numeric(x))) 0 else as.numeric(x)) -> Option A

4. Quick Check:

   Replace NA with 0 using conditional inside sapply [OK]

Hint: Use is.na(as.numeric(x)) to detect and replace [OK]

Common Mistakes:

• Not checking for NA after conversion
• Replacing numeric values incorrectly
• Confusing condition logic in if-else