Parameterized reports in R Programming - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of parameterized R Markdown report chunk

Consider this R Markdown chunk that uses a parameter n to generate a sequence. What will be the output when n = 4?

R Programming

params <- list(n = 4)
seq_output <- seq_len(params$n)
print(seq_output)

A [1] 1 2 3 4

B [1] 0 1 2 3 4

C [1] 1 2 3

D Error: object 'params' not found

💡 Hint

Remember that seq_len(n) generates a sequence from 1 to n.

The parameter n is set to 4, so seq_len(4) produces the sequence 1, 2, 3, 4. Printing it shows [1] 1 2 3 4.

🧠 Conceptual

intermediate

Purpose of parameters in R Markdown reports

What is the main purpose of using parameters in R Markdown reports?

A To speed up report rendering by caching results

B To convert R Markdown files into HTML only

C To automatically generate plots without user input

D To allow dynamic input values that change report output without editing code

💡 Hint

Think about how parameters help customize reports.

Parameters let users provide inputs that change the report's content or calculations without modifying the code itself.

🔧 Debug

advanced

Identify the error in parameter usage

This R Markdown snippet tries to use a parameter year to filter data but causes an error. What is the error?

R Programming

params <- list(year = 2023)
data <- data.frame(year = c(2022, 2023, 2024), value = c(10, 20, 30))
filtered <- subset(data, year == year)
print(filtered)

A The parameter 'year' is not defined before use

B The filter condition uses the same name 'year' for column and parameter causing ambiguity

C The subset function is misspelled

D The data frame 'data' is empty

💡 Hint

Check variable names in the filter condition carefully.

The condition 'year == year' compares the column 'year' to itself, always TRUE. To compare to the parameter, use 'year == params$year'.

📝 Syntax

advanced

Correct syntax to define parameters in YAML header

Which YAML header snippet correctly defines a parameter threshold with default value 10 for an R Markdown report?

A

params:
  - threshold: 10

B

parameters:
  threshold = 10

C

params:
  threshold: 10

D

parameters:
  threshold: "10"

💡 Hint

YAML uses key-value pairs with colon and indentation.

The correct syntax uses 'params:' followed by the parameter name and value with proper indentation and colon.

🚀 Application

expert

How many rows will the filtered data have?

Given this R code in a parameterized report with parameter min_val = 15, how many rows will filtered_data contain?

R Programming

params <- list(min_val = 15)
data <- data.frame(id = 1:5, score = c(10, 15, 20, 25, 30))
filtered_data <- subset(data, score > params$min_val)
print(nrow(filtered_data))

A 3

B 2

C 4

D 1

💡 Hint

Count how many scores are strictly greater than 15.

Scores greater than 15 are 20, 25, and 30, so filtered_data has 3 rows.