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.

Practice

1. What is the main purpose of using parameterized reports in R Markdown?

easy

A. To speed up the knitting process

B. To customize report content without changing the code

C. To automatically generate plots

D. To create interactive dashboards

Solution

1. Step 1: Understand parameterized reports concept

   Parameterized reports allow passing different inputs to the same report code.

2. Step 2: Identify the main benefit

   This lets you customize the report output without editing the code itself.

3. Final Answer:

   To customize report content without changing the code -> Option B

4. Quick Check:

   Parameterized reports = customize content without code change [OK]

Hint: Think: change inputs, not code, to customize reports [OK]

Common Mistakes:

• Confusing parameterized reports with speeding up knitting
• Thinking it automatically creates plots
• Mixing with dashboard creation

2. Which YAML header syntax correctly defines a parameter named year with default value 2023?

easy

A. params:
year: "2023"

B. parameters:
year = 2023

C. parameters:
year: 2023

D. params:
year: 2023

Solution

1. Step 1: Recall YAML parameter syntax in R Markdown

   Parameters are defined under params: with key-value pairs.

2. Step 2: Check correct key and value format

   params: year: 2023 uses params: and year: 2023 correctly without quotes needed for numbers.

3. Final Answer:

   params: year: 2023 -> Option D

4. Quick Check:

   YAML params use 'params:' and colon syntax [OK]

Hint: Use 'params:' and colon, no equals sign in YAML [OK]

Common Mistakes:

• Using 'parameters:' instead of 'params:'
• Using equals sign '=' instead of colon ':'
• Putting numbers in quotes unnecessarily

3. Given this R Markdown snippet, what will be the output when params$region is set to "West"?

```{r}
if (params$region == "West") {
  print("Sales are high in the West")
} else {
  print("Sales data not available")
}
```

medium

A. [1] "Sales are high in the West"

B. [1] "Sales data not available"

C. Error: object 'params' not found

D. [1] "Sales are high in the East"

Solution

1. Step 1: Check the condition with given parameter

   The condition checks if params$region equals "West". It is set to "West".

2. Step 2: Determine which print statement runs

   Since condition is true, it prints "Sales are high in the West".

3. Final Answer:

   [1] "Sales are high in the West" -> Option A

4. Quick Check:

   params$region == "West" -> print message for West [OK]

Hint: Match param value exactly to choose output branch [OK]

Common Mistakes:

• Confusing the else branch output
• Assuming params is undefined causing error
• Mixing region names in output

4. Identify the error in this R Markdown YAML header for parameterized report:

---
title: "Sales Report"
params:
  month = "January"
output: html_document
---

medium

A. Incorrect output format specified

B. Missing quotes around 'January'

C. Using '=' instead of ':' to assign parameter value

D. Missing 'params' section

Solution

1. Step 1: Review YAML parameter syntax

   Parameters use colon ':' to assign values, not equals '='.

2. Step 2: Identify the syntax error

   Here, month = "January" uses '=' which is invalid YAML syntax.

3. Final Answer:

   Using '=' instead of ':' to assign parameter value -> Option C

4. Quick Check:

   YAML params need ':' not '=' [OK]

Hint: YAML uses colon ':' for key-value pairs, never '=' [OK]

Common Mistakes:

• Using '=' instead of ':' in YAML
• Thinking quotes are mandatory for strings
• Confusing output format with params syntax

5. You want to create a parameterized report that filters a dataset by category and year. Which approach correctly uses parameters in the R code chunk to filter df?

hard

A. filtered_df <- subset(df, category == params$category & year == params$year)

B. filtered_df <- df[df$category = params$category & df$year = params$year, ]

C. filtered_df <- filter(df, category = params$category, year = params$year)

D. filtered_df <- df[category == params$category & year == params$year]

Solution

1. Step 1: Understand filtering syntax in R

   The subset() function uses logical conditions with '==' to filter rows.

2. Step 2: Check parameter usage in filtering

   filtered_df <- subset(df, category == params$category & year == params$year) correctly uses params$category and params$year with '==' inside subset().

3. Final Answer:

   filtered_df <- subset(df, category == params$category & year == params$year) -> Option A

4. Quick Check:

   Use '==' for comparison and subset() for filtering [OK]

Hint: Use subset() with '==' and params$ for filtering [OK]

Common Mistakes:

• Using '=' instead of '==' for comparison
• Incorrect subsetting syntax without dataframe reference
• Confusing filter() syntax without library