CSV library basics in Ruby - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to require the CSV library.

Ruby

require '[1]'

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

Anet/http

Bcsv

Cjson

Ddate

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'CSV' with uppercase letters.

Forgetting to require the library before using it.

The CSV library is included by requiring 'csv'. This makes CSV methods available.

2fill in blank

medium

Complete the code to read a CSV file named 'data.csv' and print each row.

Ruby

CSV.foreach('data.csv') do |[1]|
  puts [1].inspect
end

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

Aline

Bcsv

Cfile

Drow

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'file' which is the whole file, not a row.

Using 'csv' which is the library name, not the row variable.

CSV.foreach reads each row and yields it to the block as 'row'.

3fill in blank

hard

Fix the error in the code to parse CSV data from a string.

Ruby

data = "name,age\nAlice,30\nBob,25"
rows = CSV.[1](data)
rows.each { |row| puts row[0] }

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

Aparse

Bread

Copen

Dforeach

Attempts:

3 left

💡 Hint

Common Mistakes

Using CSV.foreach which expects a filename.

Using CSV.read which also expects a file.

CSV.parse reads CSV data from a string. CSV.foreach is for files.

4fill in blank

hard

Fill both blanks to create a hash from CSV rows with headers.

Ruby

CSV.foreach('data.csv', headers: true) do |[1]|
  person = [2].to_h
  puts person
end

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

Arow

Bline

Attempts:

3 left

💡 Hint

Common Mistakes

Using different variable names in the block and inside the block.

Forgetting to convert the row to a hash.

Each row is yielded as 'row'. Calling to_h converts it to a hash with headers as keys.

5fill in blank

hard

Fill all three blanks to write CSV data with headers.

Ruby

CSV.open('output.csv', 'w', write_headers: true, headers: [[1]]) do |csv|
  csv.[2]([[3]])
end

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

A"name", "age"

Bputs

C"Alice", 30

D <<

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'puts' instead of '<<' to add rows.

Not providing headers as strings.

Not passing row data as an array.

Headers are given as an array of strings. To add a row, use the '<<' operator with an array of values.

Practice

1. What does the Ruby CSV method CSV.foreach do?

easy

A. Reads a CSV file line by line, yielding each row as an array.

B. Writes data to a CSV file line by line.

C. Converts a CSV file into a hash with headers as keys.

D. Deletes a CSV file from the system.

Solution

1. Step 1: Understand CSV.foreach purpose

   The method CSV.foreach is designed to read CSV files line by line.

2. Step 2: Identify the output format

   Each line is yielded as an array of strings representing the cells in that row.

3. Final Answer:

   Reads a CSV file line by line, yielding each row as an array. -> Option A

4. Quick Check:

   CSV.foreach reads lines as arrays [OK]

Hint: Remember: foreach reads rows, open writes rows [OK]

Common Mistakes:

• Confusing reading with writing methods
• Thinking it returns a hash instead of an array
• Assuming it deletes files

2. Which of the following is the correct syntax to open a CSV file for writing in Ruby?

easy

A. CSV.read('file.csv', 'w')

B. CSV.open('file.csv', 'r') do |csv| ... end

C. CSV.foreach('file.csv') do |csv| ... end

D. CSV.open('file.csv', 'w') do |csv| ... end

Solution

1. Step 1: Identify mode for writing

   To write to a CSV file, the mode should be 'w' (write mode).

2. Step 2: Match syntax with CSV.open

   The correct syntax is CSV.open('file.csv', 'w') do |csv| ... end to open for writing.

3. Final Answer:

   CSV.open('file.csv', 'w') do |csv| ... end -> Option D

4. Quick Check:

   Open with 'w' writes CSV [OK]

Hint: Use 'w' mode with CSV.open to write files [OK]

Common Mistakes:

• Using 'r' mode which is for reading
• Using CSV.foreach for writing
• Using CSV.read with mode argument

3. What will be the output of this Ruby code?

require 'csv'
CSV.foreach('data.csv') do |row|
  puts row.inspect
end

Assuming data.csv contains:

name,age
Alice,30
Bob,25

medium

A. Error: CSV.foreach requires a block

B. ["name", "age"]\n["Alice", "30"]\n["Bob", "25"]

C. ["name,age"]\n["Alice,30"]\n["Bob,30"]

D. name,age\nAlice,30\nBob,25

Solution

1. Step 1: Understand CSV.foreach behavior

   It reads each line and yields an array of strings split by commas.

2. Step 2: Analyze puts row.inspect output

   Using puts row.inspect prints the array representation of each row.

3. Final Answer:

   ["name", "age"]\n["Alice", "30"]\n["Bob", "25"] -> Option B

4. Quick Check:

   CSV.foreach yields arrays, inspect shows arrays [OK]

Hint: CSV.foreach yields arrays; inspect shows array format [OK]

Common Mistakes:

• Expecting raw CSV string output
• Confusing puts with print
• Missing block for CSV.foreach

4. Identify the error in this Ruby code snippet:

require 'csv'
CSV.open('output.csv', 'w') do |csv|
  csv << 'name,age'
  csv << ['Alice', 30]
end

medium

A. The first csv << should be an array, not a string.

B. Missing require statement for CSV library.

C. The file mode 'w' is invalid for CSV.open.

D. csv << cannot accept arrays.

Solution

1. Step 1: Check CSV.open usage for writing rows

   CSV expects each row as an array of fields, not a single string.

2. Step 2: Identify the incorrect row format

   The line csv << 'name,age' should be csv << ['name', 'age'] to write two columns.

3. Final Answer:

   The first csv << should be an array, not a string. -> Option A

4. Quick Check:

   CSV rows must be arrays [OK]

Hint: Write rows as arrays, not comma strings [OK]

Common Mistakes:

• Passing a string instead of array for a row
• Forgetting to require 'csv'
• Using wrong file mode

5. You want to read a CSV file and create a hash where the first column is the key and the second column is the value. Which Ruby code correctly does this using the CSV library?

hard

A. hash = CSV.read('file.csv').to_h

B. hash = CSV.open('file.csv', 'w') { |csv| csv.to_h }

C. hash = {}
CSV.foreach('file.csv') do |row|
hash[row[0]] = row[1]
end

D. hash = CSV.foreach('file.csv') { |row| row.to_h }

Solution

1. Step 1: Understand CSV.foreach usage for reading

   CSV.foreach reads each row as an array, allowing manual hash construction.

2. Step 2: Build hash from first and second columns

   Assigning hash[row[0]] = row[1] correctly maps keys to values.

3. Final Answer:

   hash = {} CSV.foreach('file.csv') do |row| hash[row[0]] = row[1] end -> Option C

4. Quick Check:

   foreach + manual hash build = correct [OK]

Hint: Use foreach and assign hash keys manually [OK]

Common Mistakes:

• Using CSV.read.to_h which doesn't convert arrays to hash
• Using CSV.open with 'w' mode for reading
• Expecting row.to_h to work directly