File.readlines for line-by-line in Ruby - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to read all lines from a file named 'data.txt' into an array.

Ruby

lines = File.[1]('data.txt')

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

Agets

Bread

Copen

Dreadlines

Attempts:

3 left

💡 Hint

Common Mistakes

Using File.read returns the whole file as a single string, not an array of lines.

Using File.open returns a file object, not the lines directly.

The File.readlines method reads all lines from the file and returns them as an array.

2fill in blank

medium

Complete the code to print each line from the file 'notes.txt' using File.readlines.

Ruby

File.[1]('notes.txt').each do |line|
  puts line
end

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

Areadlines

Bforeach

Copen

Dread

Attempts:

3 left

💡 Hint

Common Mistakes

Using File.read returns a string, which does not have an each method for lines.

Using File.foreach reads lines one by one but is not called on File.readlines.

File.readlines reads all lines into an array, which you can then iterate over with each.

3fill in blank

hard

Fix the error in the code to correctly read lines from 'log.txt' and print them.

Ruby

lines = File.[1]('log.txt')
lines.each do |line|
  puts line
end

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

Aread

Breadlines

Copen

Dgets

Attempts:

3 left

💡 Hint

Common Mistakes

Using File.read returns a string, which cannot be iterated line by line with each.

Using File.open returns a file object, not an array of lines.

File.readlines returns an array of lines, so you can iterate over it with each.

4fill in blank

hard

Fill both blanks to create a hash with line numbers as keys and lines as values from 'input.txt'.

Ruby

lines = File.[1]('input.txt')
line_hash = lines.each_with_index.to_h { |[2], i| [i + 1, [2]] }

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

Areadlines

Bline

Dread

Attempts:

3 left

💡 Hint

Common Mistakes

Using File.read instead of File.readlines returns a string, which does not work with each_with_index as expected.

Using a wrong variable name in the block causes errors.

File.readlines reads all lines into an array. Using each_with_index with a block lets you create a hash with line numbers as keys.

5fill in blank

hard

Fill all three blanks to create a hash with uppercase line keys and their lengths as values from 'file.txt'.

Ruby

lines = File.[1]('file.txt')
result = lines.to_h { |[2]| [[2].upcase, [3] ] }

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

Aread

Breadlines

Cline.length

Dline

Attempts:

3 left

💡 Hint

Common Mistakes

Using File.read returns a string, which cannot be iterated like an array.

Mixing variable names or forgetting to call upcase causes errors.

File.readlines reads lines into an array. Using to_h with a block creates a hash with uppercase lines as keys and their lengths as values.

Practice

1. What does File.readlines('example.txt') return in Ruby?

easy

A. A hash with line numbers as keys and lines as values

B. A string containing the entire file content

C. An array where each element is a line from the file, including newline characters

D. An integer representing the number of lines in the file

Solution

1. Step 1: Understand File.readlines behavior

   File.readlines reads the whole file and returns an array of lines.

2. Step 2: Check line content format

   Each line includes the newline character at the end unless removed by chomp.

3. Final Answer:

   An array where each element is a line from the file, including newline characters -> Option C

4. Quick Check:

   File.readlines returns array of lines [OK]

Hint: Remember: File.readlines returns an array of lines with newlines [OK]

Common Mistakes:

• Thinking it returns a single string
• Assuming it returns a hash or dictionary
• Believing it returns just the line count

2. Which of the following is the correct syntax to read all lines from a file named data.txt into an array in Ruby?

easy

A. File.read_lines[]('data.txt')

B. File.read('data.txt')

C. File.read_lines('data.txt')

D. File.readlines('data.txt')

Solution

1. Step 1: Recall correct method name

   The correct Ruby method to read lines is File.readlines (no underscore or plural misspelling).

2. Step 2: Check method call syntax

   The method is called with parentheses and the filename as a string argument.

3. Final Answer:

   File.readlines('data.txt') -> Option D

4. Quick Check:

   Correct method name and syntax = File.readlines('data.txt') [OK]

Hint: Use exact method name: File.readlines('filename') [OK]

Common Mistakes:

• Using underscores instead of camel case
• Misspelling the method name
• Omitting parentheses or using wrong brackets

3. Given a file notes.txt with these lines:

Line 1
Line 2
Line 3

What will the following Ruby code output?

lines = File.readlines('notes.txt')
puts lines[1]

medium

A. Line 2

B. Line 1

C. Line 3

D. nil

Solution

1. Step 1: Understand File.readlines output

   The file lines are read into an array: ["Line 1\n", "Line 2\n", "Line 3\n"].

2. Step 2: Access the second element

   Array indexing starts at 0, so lines[1] is "Line 2\n".

3. Final Answer:

   Line 2 -> Option A

4. Quick Check:

   Index 1 = second line = Line 2 [OK]

Hint: Remember arrays start at 0; lines[1] is second line [OK]

Common Mistakes:

• Assuming indexing starts at 1
• Forgetting newline characters affect output
• Expecting nil for valid index

4. What is wrong with this Ruby code snippet?

lines = File.readlines('file.txt')
lines.each do |line|
  puts line.chomp
end

Assuming file.txt exists and is readable.

medium

A. It will skip the first line of the file

B. Nothing is wrong; it correctly prints each line without newlines

C. It will print lines with extra newlines

D. It will raise an error because chomp is not a method

Solution

1. Step 1: Analyze File.readlines usage

   File.readlines reads all lines into an array, each ending with a newline.

2. Step 2: Check iteration and chomp usage

   Using each to iterate and chomp removes trailing newline before printing.

3. Final Answer:

   Nothing is wrong; it correctly prints each line without newlines -> Option B

4. Quick Check:

   chomp removes newline, so output is clean [OK]

Hint: Use chomp to remove newlines when printing lines [OK]

Common Mistakes:

• Thinking chomp is invalid method
• Expecting extra newlines despite chomp
• Assuming lines are skipped

5. You want to read a file data.txt and create a new array containing only lines that include the word "error" (case insensitive). Which Ruby code correctly does this using File.readlines?

hard

A. File.readlines('data.txt').select { |line| line.downcase.include?('error') }

B. File.readlines('data.txt').map { |line| line.include?('error') }

C. File.readlines('data.txt').filter { |line| line.include?('Error') }

D. File.readlines('data.txt').reject { |line| line.downcase.include?('error') }

Solution

1. Step 1: Use File.readlines to get all lines

   This returns an array of lines from the file.

2. Step 2: Filter lines case-insensitively

   Use select to keep lines where line.downcase.include?('error') is true.

3. Step 3: Check other options

   File.readlines('data.txt').map { |line| line.include?('error') } uses map which returns booleans, not lines. File.readlines('data.txt').filter { |line| line.include?('Error') } checks case-sensitive 'Error'. File.readlines('data.txt').reject { |line| line.downcase.include?('error') } rejects lines with 'error', opposite of requirement.

4. Final Answer:

   File.readlines('data.txt').select { |line| line.downcase.include?('error') } -> Option A

5. Quick Check:

   select + downcase + include? = correct filter [OK]

Hint: Use select with downcase and include? for case-insensitive filtering [OK]

Common Mistakes:

• Using map instead of select
• Ignoring case sensitivity
• Using reject instead of select