readRDS and saveRDS in R Programming - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to save the object data to a file.

R Programming

saveRDS(data, [1])

Drag options to blanks, or click blank then click option'

A"datafile.txt"

B"datafile.rds"

Cdatafile.rds

Ddatafile

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting to put the file name in quotes.

Using a wrong file extension like .txt.

The saveRDS function requires the file name as a string, so it must be in quotes.

2fill in blank

medium

Complete the code to read the saved RDS file into the variable loaded_data.

R Programming

loaded_data <- [1]("datafile.rds")

Drag options to blanks, or click blank then click option'

AreadRDS

Bread.csv

Cload

Dscan

Attempts:

3 left

💡 Hint

Common Mistakes

Using load which is for .RData files, not .rds.

Using read.csv which is for CSV files.

The readRDS function reads an RDS file and returns the saved object.

3fill in blank

hard

Fix the error in the code to correctly save the variable my_list to a file.

R Programming

saveRDS([1], "mylist.rds")

Drag options to blanks, or click blank then click option'

Amylist

B"my_list"

Cmy_list

Dlist

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong variable name without underscore.

Putting the variable name in quotes.

The variable name is my_list, so it must be used exactly without quotes.

4fill in blank

hard

Fill both blanks to save df to a file and then read it back into df_copy.

R Programming

saveRDS([1], [2])
df_copy <- readRDS("dataframe.rds")

Drag options to blanks, or click blank then click option'

Adf

B"dataframe.rds"

Cdf_copy

D"df.rds"

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping the object and file name.

Not using quotes around the file name.

You save the object df to the file named "dataframe.rds" before reading it back.

5fill in blank

hard

Fill all three blanks to save results to a file, read it back into loaded_results, and check if they are identical.

R Programming

saveRDS([1], [2])
loaded_results <- [3]("results.rds")
identical(results, loaded_results)

Drag options to blanks, or click blank then click option'

Aresults

B"results.rds"

CreadRDS

Dload

Attempts:

3 left

💡 Hint

Common Mistakes

Using load instead of readRDS.

Not using quotes around the file name.

You save results to "results.rds", then read it back with readRDS to compare.

Practice

1. What does the saveRDS() function do in R?

easy

A. It creates a new R script file.

B. It reads data from a CSV file.

C. It saves a single R object to a file.

D. It deletes an R object from memory.

Solution

1. Step 1: Understand the purpose of saveRDS()

   The saveRDS() function is used to save one R object to a file in a binary format.

2. Step 2: Compare with other options

   The other options describe unrelated actions: creating a new R script file, reading data from a CSV file, or deleting an R object from memory.

3. Final Answer:

   It saves a single R object to a file. -> Option C

4. Quick Check:

   saveRDS() = saves object [OK]

Hint: saveRDS saves one object to a file in R [OK]

Common Mistakes:

• Confusing saveRDS() with read.csv()
• Thinking saveRDS() saves multiple objects at once
• Assuming saveRDS() creates scripts

2. Which of the following is the correct syntax to save an object my_data to a file named data.rds?

easy

A. saveRDS(my_data, "data.rds")

B. saveRDS("data.rds", my_data)

C. readRDS(my_data, "data.rds")

D. save(my_data, file = "data.rds")

Solution

1. Step 1: Recall saveRDS() argument order

   The first argument is the object to save, the second is the file name as a string.

2. Step 2: Check each option

   saveRDS(my_data, "data.rds") matches the correct order. saveRDS("data.rds", my_data) reverses arguments. readRDS(my_data, "data.rds") uses readRDS which is for reading, not saving. save(my_data, file = "data.rds") uses save(), which is different.

3. Final Answer:

   saveRDS(my_data, "data.rds") -> Option A

4. Quick Check:

   saveRDS(object, file) = correct syntax [OK]

Hint: Remember: saveRDS(object, "filename") [OK]

Common Mistakes:

• Swapping object and filename arguments
• Using readRDS() instead of saveRDS() to save
• Confusing saveRDS() with save()

3. What will be the output of the following R code?

my_list <- list(a = 1, b = 2)
saveRDS(my_list, "mylist.rds")
loaded_list <- readRDS("mylist.rds")
print(loaded_list$b)

medium

A. Error: object not found

B. 1

C. NULL

D. 2

Solution

1. Step 1: Understand saving and loading

   The list my_list has elements a=1 and b=2. It is saved to a file and then loaded back into loaded_list.

2. Step 2: Access element b of loaded_list

   Accessing loaded_list$b retrieves the value 2, as saved.

3. Final Answer:

   2 -> Option D

4. Quick Check:

   readRDS() loads saved object correctly [OK]

Hint: readRDS loads saved object exactly as saved [OK]

Common Mistakes:

• Expecting print to show 1 instead of 2
• Thinking readRDS returns NULL
• Confusing saveRDS and readRDS usage

4. Identify the error in this R code snippet:

saveRDS(data, "datafile.rds")
new_data <- readRDS(datafile.rds)
print(new_data)

medium

A. Missing quotes around filename in readRDS()

B. Using saveRDS() instead of save()

C. Incorrect object name in saveRDS()

D. No error, code runs fine

Solution

1. Step 1: Check readRDS() argument

   The filename must be a string, so it needs quotes around it.

2. Step 2: Identify the error

   In readRDS(datafile.rds), the filename is unquoted, causing an error.

3. Final Answer:

   Missing quotes around filename in readRDS() -> Option A

4. Quick Check:

   Filename must be a string in readRDS() [OK]

Hint: Always put filename in quotes in readRDS() [OK]

Common Mistakes:

• Forgetting quotes around filename
• Confusing saveRDS() and save()
• Assuming no error when filename is unquoted

5. You saved a data frame df using saveRDS(df, "df.rds"). Later, you want to load it and add a new column status with value "active" for all rows. Which code correctly does this?

hard

A. df <- saveRDS("df.rds")
df$status <- "active"

B. df <- readRDS("df.rds")
df$status <- "active"
saveRDS(df, "df.rds")

C. readRDS(df, "df.rds")
df$status <- "active"

D. df <- readRDS("df.rds")
addColumn(df, status = "active")

Solution

1. Step 1: Load the saved data frame

   Use df <- readRDS("df.rds") to load the saved object into df.

2. Step 2: Add new column and save again

   Add the new column by df$status <- "active" and save the updated object back with saveRDS(df, "df.rds").

3. Final Answer:

   df <- readRDS("df.rds") df$status <- "active" saveRDS(df, "df.rds") -> Option B

4. Quick Check:

   Load, modify, then save again [OK]

Hint: Load with readRDS, modify, then saveRDS to update file [OK]

Common Mistakes:

• Using saveRDS() to load data
• Forgetting to save after modification
• Using incorrect function to add column