JSON with jsonlite in R Programming - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this JSON conversion?

Consider this R code using jsonlite:

library(jsonlite)
my_list <- list(name = "Alice", age = 30, scores = c(90, 85, 88))
json_text <- toJSON(my_list, auto_unbox = TRUE)
cat(json_text)

What is the exact output printed by cat(json_text)?

R Programming

library(jsonlite)
my_list <- list(name = "Alice", age = 30, scores = c(90, 85, 88))
json_text <- toJSON(my_list, auto_unbox = TRUE)
cat(json_text)

A ["Alice",30,[90,85,88]]

B {"name":"Alice","age":30,"scores":[90,85,88]}

C {"name":["Alice"],"age":[30],"scores":[90,85,88]}

D {"name":"Alice","age":"30","scores":[90,85,88]}

💡 Hint

Remember that auto_unbox = TRUE removes array brackets for single values.

The toJSON function with auto_unbox = TRUE converts single values like name and age to JSON scalars, not arrays. The scores vector remains an array.

❓ Predict Output

intermediate

What does this JSON parsing produce?

Given this R code:

library(jsonlite)
json_str <- '{"fruit":"apple","count":5,"colors":["red","green"]}'
parsed <- fromJSON(json_str)
str(parsed)

What is the structure printed by str(parsed)?

R Programming

library(jsonlite)
json_str <- '{"fruit":"apple","count":5,"colors":["red","green"]}'
parsed <- fromJSON(json_str)
str(parsed)

A

List of 3
 $ fruit : chr "apple"
 $ count : int 5
 $ colors: chr [1:2] "red" "green"

B

List of 3
 $ fruit : chr [1:1] "apple"
 $ count : chr "5"
 $ colors: list of 2

C

List of 3
 $ fruit : chr "apple"
 $ count : chr "5"
 $ colors: chr [1:2] "red" "green"

D

List of 3
 $ fruit : chr "apple"
 $ count : int 5
 $ colors: list of 1

💡 Hint

Check how fromJSON converts JSON arrays and numbers.

fromJSON converts JSON strings to character vectors, numbers to integers, and JSON arrays to vectors or lists depending on content. Here colors is a character vector of length 2.

🔧 Debug

advanced

Why does this JSON conversion fail?

This R code throws an error:

library(jsonlite)
my_data <- list(a = 1, b = function(x) x + 1)
toJSON(my_data)

What is the cause of the error?

R Programming

library(jsonlite)
my_data <- list(a = 1, b = function(x) x + 1)
toJSON(my_data)

A The list is missing names for elements, causing a syntax error.

B toJSON requires numeric vectors only, so the integer 1 causes an error.

C jsonlite cannot convert functions to JSON, causing an error.

D The function argument x is undefined, causing a runtime error.

💡 Hint

Think about what data types JSON supports.

JSON format cannot represent functions. jsonlite throws an error when trying to convert a function object.

📝 Syntax

advanced

Which option correctly parses nested JSON?

Given this JSON string:

{"person":{"name":"Bob","age":25},"hobbies":["reading","swimming"]}

Which R code correctly parses it into a list with nested elements?

A fromJSON('{"person":{"name":"Bob","age":25},"hobbies":reading,swimming}')

B fromJSON('{person:{name:"Bob",age:25},hobbies:["reading","swimming"]}')

C fromJSON('{"person":{"name":"Bob","age":25},"hobbies":[reading,swimming]}')

D fromJSON('{"person":{"name":"Bob","age":25},"hobbies":["reading","swimming"]}')

💡 Hint

Check JSON syntax rules for strings and keys.

Option D uses valid JSON syntax with double quotes around keys and string values. Others have missing quotes or invalid JSON.

🚀 Application

expert

How many elements are in the parsed JSON array?

This R code parses a JSON array:

library(jsonlite)
json_arr <- '[{"id":1,"val":10},{"id":2,"val":20},{"id":3,"val":30}]'
parsed <- fromJSON(json_arr)
length(parsed)

What is the value of length(parsed)?

R Programming

library(jsonlite)
json_arr <- '[{"id":1,"val":10},{"id":2,"val":20},{"id":3,"val":30}]'
parsed <- fromJSON(json_arr)
length(parsed)

A 2

B 3

C 6

D 1

💡 Hint

Check the structure of parsed data and what length() returns for data frames.

fromJSON converts the JSON array of objects into a data frame with 3 rows and 2 columns. length() on a data frame returns the number of columns, which is 2.