readRDS and saveRDS in R Programming - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this R code using saveRDS and readRDS?

Consider the following R code that saves and reads an object:

my_list <- list(a = 1, b = 2)
saveRDS(my_list, file = "temp.rds")
new_list <- readRDS("temp.rds")
print(new_list$b)

What will be printed?

R Programming

my_list <- list(a = 1, b = 2)
saveRDS(my_list, file = "temp.rds")
new_list <- readRDS("temp.rds")
print(new_list$b)

A 2

B NULL

C Error: object 'new_list' not found

D 1

💡 Hint

Remember that saveRDS saves the object exactly and readRDS reads it back as is.

The object my_list is saved to a file and then read back into new_list. Accessing new_list$b returns 2, the value stored under key 'b'.

🧠 Conceptual

intermediate

What does saveRDS() do in R?

Which of the following best describes the purpose of saveRDS() in R?

A Converts an R object to a CSV file

B Saves an R object to a file in a binary format for later use

C Reads an R object from a file and loads it into the global environment

D Saves all variables in the current environment to a text file

💡 Hint

Think about what saveRDS() stores and how it differs from save().

saveRDS() saves a single R object to a file in a binary format. It does not save the entire environment or convert to text formats.

🔧 Debug

advanced

Why does this code cause an error when reading an RDS file?

Look at this R code:

saveRDS(42, file = "number.rds")
num <- readRDS("number.txt")
print(num)

What error will occur and why?

A Error: object 'num' not found

B No error, prints 42

C Error: cannot open the connection to 'number.txt' because the file does not exist

D Error: invalid R object in 'number.txt'

💡 Hint

Check the file names used in saving and reading.

The file was saved as 'number.rds' but the code tries to read 'number.txt', which does not exist, causing a file connection error.

📝 Syntax

advanced

Which option correctly saves and reads an R object?

Which of the following code snippets correctly saves an object df and reads it back into df2?

A

saveRDS(df, "data.rds")
df2 <- readRDS("data.rds")

B

saveRDS(df)
df2 <- readRDS()

C

saveRDS(df, "data.txt")
df2 <- readRDS("data.txt")

D

saveRDS(df, file = "data.rds")
df2 <- readRDS(file = "data.rds")

💡 Hint

Check the correct argument names and file extensions.

Option D uses the correct argument file= and proper file extension .rds. Option D misses the argument name, which is allowed but less clear. Option D uses wrong extension, and B misses file arguments.

🚀 Application

expert

How many objects are saved and restored using saveRDS and readRDS?

Given the following R code:

a <- 10
b <- 20
saveRDS(a, file = "a.rds")
saved_obj <- readRDS("a.rds")

How many objects are saved and restored by saveRDS and readRDS?

A One object: only 'a' is saved and restored

B Two objects: both 'a' and 'b' are saved and restored

C No objects are saved because 'b' is not saved explicitly

D All objects in the environment are saved and restored

💡 Hint

Remember what saveRDS saves compared to save.

saveRDS saves only the single object passed to it, here 'a'. The object 'b' is not saved or restored.