read.csv and write.csv in R Programming - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to read a CSV file named 'data.csv' into a variable called df.

R Programming

df <- [1]("data.csv")

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

Awrite.table

Bwrite.csv

Cread.table

Dread.csv

Attempts:

3 left

💡 Hint

Common Mistakes

Using write.csv instead of read.csv

Using read.table without specifying separator

The read.csv function reads CSV files into R as data frames.

2fill in blank

medium

Complete the code to save the data frame df to a CSV file named 'output.csv'.

R Programming

[1](df, "output.csv")

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

Aread.csv

Bsave.csv

Cwrite.csv

Dexport.csv

Attempts:

3 left

💡 Hint

Common Mistakes

Using read.csv instead of write.csv

Using save.csv which does not exist

The write.csv function saves data frames to CSV files.

3fill in blank

hard

Fix the error in the code to read a CSV file with headers.

R Programming

df <- read.csv("data.csv", [1] = TRUE)

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

Aheader_row

Bheader

Chead

Dheaders

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'headers' instead of 'header'

Using 'head' which is a different function

The correct argument to specify that the CSV file has headers is header.

4fill in blank

hard

Fill both blanks to read a CSV file with semicolon separator and save it back with row names excluded.

R Programming

df <- read.csv("data.csv", sep = [1])
write.csv(df, "output.csv", row.names = [2])

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A";"

BTRUE

CFALSE

D","

Attempts:

3 left

💡 Hint

Common Mistakes

Using comma as separator when file uses semicolon

Setting row.names to TRUE which includes row names

To read a CSV with semicolon separator, use sep = ";". To exclude row names when saving, use row.names = FALSE.

5fill in blank

hard

Fill all three blanks to read a CSV file without converting strings to factors, then write it with UTF-8 encoding and no row names.

R Programming

df <- read.csv("data.csv", stringsAsFactors = [1])
write.csv(df, "output.csv", fileEncoding = [2], row.names = [3])

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

ATRUE

BFALSE

C"UTF-8"

D"ASCII"

Attempts:

3 left

💡 Hint

Common Mistakes

Leaving stringsAsFactors as TRUE causing factors

Using wrong encoding like ASCII

Including row names unintentionally

Set stringsAsFactors = FALSE to keep strings as characters. Use fileEncoding = "UTF-8" to write with UTF-8 encoding. Set row.names = FALSE to exclude row names.

Practice

1. What does the read.csv function do in R?

easy

A. Loads data from a CSV file into a data frame

B. Saves a data frame to a CSV file

C. Creates a new CSV file with default data

D. Deletes a CSV file from the disk

Solution

1. Step 1: Understand the purpose of read.csv

   The read.csv function is designed to read data stored in CSV files and load it into R as a data frame.

2. Step 2: Differentiate from write.csv

   write.csv saves data frames to CSV files, so it does the opposite of read.csv.

3. Final Answer:

   Loads data from a CSV file into a data frame -> Option A

4. Quick Check:

   read.csv loads CSV data [OK]

Hint: Remember: read.csv reads files, write.csv writes files [OK]

Common Mistakes:

• Confusing read.csv with write.csv
• Thinking read.csv creates new files
• Assuming read.csv deletes files

2. Which of the following is the correct syntax to save a data frame named df to a CSV file called output.csv?

easy

A. read.csv(df, file = "output.csv")

B. write.csv(df, file = "output.csv")

C. write.csv(file = df, "output.csv")

D. write.csv("output.csv", df)

Solution

1. Step 1: Recall the argument order of write.csv

   The first argument is the data frame to save, the second is the file name with the parameter file=.

2. Step 2: Check each option's argument order

   write.csv(df, file = "output.csv") correctly uses write.csv(df, file = "output.csv"). read.csv(df, file = "output.csv") uses read.csv which is for reading, not writing. Options B and D have wrong argument order.

3. Final Answer:

   write.csv(df, file = "output.csv") -> Option B

4. Quick Check:

   write.csv(data, file=filename) syntax [OK]

Hint: write.csv(data, file=filename) saves data frame [OK]

Common Mistakes:

• Swapping arguments order
• Using read.csv instead of write.csv
• Omitting the file= parameter

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

data <- data.frame(Name = c("Anna", "Bob"), Age = c(25, 30))
write.csv(data, file = "people.csv", row.names = FALSE)
read_data <- read.csv("people.csv")
print(read_data)

medium

A. Error: file not found

B. Name Age
0 Anna 25
1 Bob 30

C. Name Age
1 Anna 25
2 Bob 30
3 NA NA

D. Name Age
1 Anna 25
2 Bob 30

Solution

1. Step 1: Understand the data frame and write.csv call

   The data frame has two rows with names and ages. The write.csv saves it without row names because row.names = FALSE.

2. Step 2: Read the CSV and print

   The read.csv reads the file back, creating a data frame with default row numbers 1 and 2. Printing shows the two rows with correct data.

3. Final Answer:

   Name Age 1 Anna 25 2 Bob 30 -> Option D

4. Quick Check:

   write.csv without row.names keeps data clean [OK]

Hint: Use row.names=FALSE to avoid extra row numbers in CSV [OK]

Common Mistakes:

• Forgetting row.names=FALSE adds extra column
• Expecting zero-based row numbers
• Assuming file not found error

4. Identify the error in this code snippet:

df <- data.frame(x = 1:3, y = 4:6)
write.csv(df, "data.csv")
new_df <- read.csv(data.csv)
print(new_df)

medium

A. print() cannot display data frames

B. write.csv should not have data frame as first argument

C. Missing quotes around file name in read.csv

D. read.csv cannot read CSV files

Solution

1. Step 1: Check the write.csv usage

   write.csv(df, "data.csv") is correct syntax to save the data frame.

2. Step 2: Check the read.csv usage

   The code uses read.csv(data.csv) without quotes around the file name, which causes an error because R treats data.csv as a variable, not a string.

3. Final Answer:

   Missing quotes around file name in read.csv -> Option C

4. Quick Check:

   File names must be strings in quotes [OK]

Hint: Always put file names in quotes in read.csv and write.csv [OK]

Common Mistakes:

• Omitting quotes around file names
• Confusing argument order
• Thinking print() can't show data frames

5. You have a CSV file with missing values represented as empty cells. Which read.csv argument helps you automatically convert these empty cells to NA in R?

hard

A. na.strings = ""

B. stringsAsFactors = TRUE

C. header = FALSE

D. row.names = NULL

Solution

1. Step 1: Understand missing values in CSV

   Empty cells in CSV files often represent missing data, which R can mark as NA if told how to interpret them.

2. Step 2: Use na.strings argument

   The na.strings = "" argument tells read.csv to treat empty strings as NA values automatically.

3. Final Answer:

   na.strings = "" -> Option A

4. Quick Check:

   na.strings="" converts empty cells to NA [OK]

Hint: Use na.strings="" to read blanks as NA [OK]

Common Mistakes:

• Ignoring na.strings argument
• Using stringsAsFactors which affects factor conversion
• Confusing header or row.names with missing data handling