String formatting with sprintf in R Programming - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of sprintf with numeric formatting

What is the output of the following R code using sprintf to format numbers?

R Programming

result <- sprintf("%.2f", 3.14159)
print(result)

A "3.14"

B "3.1416"

C "3.1"

D "3.15"

💡 Hint

Remember that %.2f rounds the number to 2 decimal places.

The format %.2f rounds the number to two decimal places. 3.14159 rounded to two decimals is 3.14.

❓ Predict Output

intermediate

String padding with sprintf

What will be the output of this R code that uses sprintf to pad a string?

R Programming

result <- sprintf("%10s", "cat")
print(result)

A "cat"

B "cat "

C " cat "

D " cat"

💡 Hint

The number 10 means the total width of the string including spaces.

The format %10s right-aligns the string in a field of width 10, padding with spaces on the left.

❓ Predict Output

advanced

Multiple values formatting with sprintf

What is the output of this R code that formats multiple values with sprintf?

R Programming

result <- sprintf("Name: %s, Age: %d, Score: %.1f", "Alice", 30, 95.678)
print(result)

A "Name: Alice, Age: 30, Score: 95"

B "Name: Alice, Age: 30, Score: 95.6"

C "Name: Alice, Age: 30, Score: 95.7"

D "Name: Alice, Age: 30, Score: 95.67"

💡 Hint

%.1f rounds the number to one decimal place.

The score 95.678 rounded to one decimal place is 95.7, so the formatted string shows that.

❓ Predict Output

advanced

Using sprintf with hexadecimal formatting

What will this R code print when formatting a number as hexadecimal using sprintf?

R Programming

result <- sprintf("%x", 255)
print(result)

A "FF"

B "ff"

C "255"

D "0xff"

💡 Hint

%x formats the number as lowercase hexadecimal without prefix.

The number 255 in hexadecimal is ff in lowercase, which %x produces without 0x prefix.

🧠 Conceptual

expert

Understanding sprintf format specifiers

Which sprintf format specifier correctly formats a floating-point number with at least 8 characters wide, 3 decimal places, and left-aligned?

A "%-8.3f"

B "%8.3f"

C "%08.3f"

D "%+8.3f"

💡 Hint

The minus sign (-) left-aligns the output in the field width.

The format %-8.3f means: floating number with 3 decimals, left-aligned in 8 spaces wide field.

Practice

1. What does the sprintf function in R primarily do?

easy

A. It reads data from a file and stores it in a string.

B. It splits a string into a list of words.

C. It converts strings to uppercase letters.

D. It creates a formatted string by inserting values into placeholders.

Solution

1. Step 1: Understand the purpose of sprintf

   The sprintf function formats strings by replacing placeholders with values.

2. Step 2: Compare options with the function's purpose

   Only It creates a formatted string by inserting values into placeholders. describes this behavior correctly; others describe unrelated string operations.

3. Final Answer:

   It creates a formatted string by inserting values into placeholders. -> Option D

4. Quick Check:

   sprintf formats strings = B [OK]

Hint: Remember sprintf builds strings by filling placeholders [OK]

Common Mistakes:

• Confusing sprintf with string splitting functions
• Thinking sprintf changes case of letters
• Assuming sprintf reads files

2. Which of the following is the correct syntax to format an integer using sprintf in R?

easy

A. sprintf("%d", 42)

B. sprintf("%s", 42)

C. sprintf("%f", 42)

D. sprintf("%c", 42)

Solution

1. Step 1: Identify the placeholder for integers

   The placeholder %d is used for integers in sprintf.

2. Step 2: Match the placeholder with the value type

   Since 42 is an integer, %d is correct; %s is for strings, %f for floats, and %c for characters.

3. Final Answer:

   sprintf("%d", 42) -> Option A

4. Quick Check:

   Integer placeholder = %d [OK]

Hint: Use %d for integers, %s for strings, %f for decimals [OK]

Common Mistakes:

• Using %s for numbers instead of %d
• Using %f for integers without decimals
• Confusing %c with integer formatting

3. What is the output of this R code?

sprintf("Name: %s, Age: %d", "Alice", 30)

medium

A. "Name: %s, Age: %d"

B. "Name: Alice, Age: 30"

C. "Name: Alice, Age: %d"

D. "Name: %s, Age: 30"

Solution

1. Step 1: Match placeholders with arguments

   The first placeholder %s is replaced by "Alice" (string), the second %d by 30 (integer).

2. Step 2: Construct the final string

   Replacing placeholders gives "Name: Alice, Age: 30" as the output string.

3. Final Answer:

   "Name: Alice, Age: 30" -> Option B

4. Quick Check:

   Placeholders replaced correctly = A [OK]

Hint: Placeholders %s and %d replaced by arguments in order [OK]

Common Mistakes:

• Not replacing placeholders with values
• Mixing up %s and %d placeholders
• Outputting the format string literally

4. Identify the error in this R code:

sprintf("Value: %d", "ten")

medium

A. Incorrect use of double quotes around the format string.

B. Missing closing parenthesis in sprintf function.

C. Using %d placeholder with a string causes a type mismatch error.

D. No error; code runs correctly.

Solution

1. Step 1: Check placeholder and argument types

   The placeholder %d expects an integer, but "ten" cannot be coerced to a number, resulting in NA and a warning.

2. Step 2: Determine if it causes an error

   The code runs but produces a warning and outputs "Value: NA"; this is a type mismatch issue.

3. Final Answer:

   Using %d placeholder with a string causes a type mismatch error. -> Option C

4. Quick Check:

   Type mismatch warning occurs = A [OK]

Hint: sprintf coerces types, may produce NA and warning [OK]

Common Mistakes:

• Confusing coercion warning with type mismatch error
• Looking for missing parenthesis (it's present)
• Assuming invalid quotes (they're correct)

5. You want to format a floating-point number with exactly 2 decimal places using sprintf. Which code snippet achieves this?

hard

A. sprintf("%.2f", 3.14159)

B. sprintf("%2f", 3.14159)

C. sprintf("%f.2", 3.14159)

D. sprintf("%f", round(3.14159, 2))

Solution

1. Step 1: Understand the format for decimal precision

   The format %.2f tells sprintf to print a float with 2 digits after the decimal point.

2. Step 2: Compare options for correct syntax

   sprintf("%.2f", 3.14159) uses %.2f, which is correct. sprintf("%2f", 3.14159) misses the dot, A has incorrect syntax, and D rounds before formatting but does not guarantee 2 decimals in output.

3. Final Answer:

   sprintf("%.2f", 3.14159) -> Option A

4. Quick Check:

   Use %.2f for 2 decimals [OK]

Hint: Use %.2f to fix two decimal places in sprintf [OK]

Common Mistakes:

• Omitting the dot before precision number
• Using round() but forgetting format specifier
• Incorrect order of precision and type specifier