Map/collect for transformation in Ruby - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to transform each number by doubling it using map.

Ruby

numbers = [1, 2, 3, 4]
doubled = numbers.[1] { |n| n * 2 }
puts doubled.inspect

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

Aselect

Bmap

Ceach

Dcollect

Attempts:

3 left

💡 Hint

Common Mistakes

Using each which returns the original array without changes.

Using select which filters elements instead of transforming.

The map method transforms each element and returns a new array with the results.

2fill in blank

medium

Complete the code to convert all strings in the array to uppercase using collect.

Ruby

words = ['apple', 'banana', 'cherry']
upcased = words.[1] { |word| word.upcase }
puts upcased.inspect

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

Aeach

Bselect

Ccollect

Dreject

Attempts:

3 left

💡 Hint

Common Mistakes

Using each which does not return a transformed array.

Using select which filters elements.

The collect method is an alias for map and transforms each element.

3fill in blank

hard

Fix the error in the code to correctly transform numbers by adding 5 using map.

Ruby

nums = [10, 20, 30]
result = nums.[1] { |num| num + 5 }
puts result.inspect

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

Amap

Bselect

Ceach

Dfind

Attempts:

3 left

💡 Hint

Common Mistakes

Using each which does not transform the array.

Using select which filters elements.

map returns a new array with each element transformed. each returns the original array.

4fill in blank

hard

Fill both blanks to create a hash where keys are words and values are their lengths using map.

Ruby

words = ['dog', 'cat', 'bird']
lengths = words.[1] { |word| [word, word.[2]] }.to_h
puts lengths.inspect

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

Amap

Beach

Clength

Dsize

Attempts:

3 left

💡 Hint

Common Mistakes

Using each which does not return a transformed array.

Using size which also works but is less common than length.

map transforms each word into a key-value pair array. length returns the length of the string.

5fill in blank

hard

Fill all three blanks to transform an array of numbers into a hash with keys as strings and values as squares.

Ruby

nums = [1, 2, 3]
squares = nums.[1] { |n| [n.[2].to_s, n [3] 2] }.to_h
puts squares.inspect

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

Amap

Bto_s

C**

Deach

Attempts:

3 left

💡 Hint

Common Mistakes

Using each which does not transform the array.

Using * instead of ** for squaring.

map transforms each number into a key-value pair. to_s converts the number to a string key. ** squares the number.

Practice

1. What does the Ruby method map (or collect) do to an array?

easy

A. It sorts the array in ascending order.

B. It deletes items from the original array.

C. It creates a new array by changing each item based on the block given.

D. It returns the first item of the array.

Solution

1. Step 1: Understand the purpose of map

   The map method takes each item in the array and applies the block's code to it.

2. Step 2: Result of map

   This creates a new array with the changed items, leaving the original array unchanged.

3. Final Answer:

   It creates a new array by changing each item based on the block given. -> Option C

4. Quick Check:

   map changes items and returns new array [OK]

Hint: Remember: map returns a new changed array, original stays same [OK]

Common Mistakes:

• Thinking map changes the original array
• Confusing map with delete or sort methods
• Believing map returns a single value

2. Which of the following is the correct syntax to double each number in the array [1, 2, 3] using map?

easy

A. [1, 2, 3].map { |x| x * 2 }

B. [1, 2, 3].map(x => x * 2)

C. [1, 2, 3].map do x x * 2 end

D. [1, 2, 3].map { x -> x * 2 }

Solution

1. Step 1: Identify correct block syntax

   In Ruby, map uses a block with { |variable| code } or do |variable| code end.

2. Step 2: Check each option

   [1, 2, 3].map { |x| x * 2 } uses correct block syntax with { |x| x * 2 }. Others have syntax errors or wrong block format.

3. Final Answer:

   [1, 2, 3].map { |x| x * 2 } -> Option A

4. Quick Check:

   Use curly braces and pipe for block variables [OK]

Hint: Use { |var| ... } for map blocks in one line [OK]

Common Mistakes:

• Missing pipes around block variable
• Using arrow syntax like JavaScript
• Incorrect do-end block without pipes

3. What is the output of this Ruby code?

[4, 5, 6].map { |n| n + 1 }

medium

A. [4, 5, 6]

B. Error: undefined method

C. [3, 4, 5]

D. [5, 6, 7]

Solution

1. Step 1: Understand the block operation

   The block adds 1 to each number in the array: 4+1=5, 5+1=6, 6+1=7.

2. Step 2: Result of map

   The map method returns a new array with these values: [5, 6, 7].

3. Final Answer:

   [5, 6, 7] -> Option D

4. Quick Check:

   Each item +1 = [5, 6, 7] [OK]

Hint: Add inside block to transform each item [OK]

Common Mistakes:

• Expecting original array to change
• Confusing map with each (which returns original array)
• Thinking map returns a single value

4. Find the error in this code snippet:

numbers = [1, 2, 3]
numbers.map { n n * 2 }

medium

A. The block should use parentheses

B. Missing pipe symbols around block variable

C. map cannot be used on arrays

D. The array should be a hash

Solution

1. Step 1: Check block syntax

   The block is missing pipes around the variable: it should be { |n| n * 2 }.

2. Step 2: Understand Ruby block rules

   Without pipes, Ruby does not know the block variable, causing a syntax error.

3. Final Answer:

   Missing pipe symbols around block variable -> Option B

4. Quick Check:

   Always use |var| in map blocks [OK]

Hint: Always put pipes | | around block variables [OK]

Common Mistakes:

• Omitting pipes in block parameters
• Thinking map is invalid on arrays
• Trying to use parentheses instead of pipes

5. Given an array of strings ["apple", "banana", "cherry"], how do you use map to create a new array with the length of each string?

hard

A. ["apple", "banana", "cherry"].map { |fruit| fruit.length }

B. ["apple", "banana", "cherry"].map { |fruit| fruit.upcase }

C. ["apple", "banana", "cherry"].map { |fruit| fruit[0] }

D. ["apple", "banana", "cherry"].map { |fruit| fruit.reverse }

Solution

1. Step 1: Identify the desired transformation

   We want the length of each string, so we use fruit.length inside the block.

2. Step 2: Apply map with correct block

   Using map { |fruit| fruit.length } returns a new array of lengths.

3. Final Answer:

   ["apple", "banana", "cherry"].map { |fruit| fruit.length } -> Option A

4. Quick Check:

   Map each string to its length [OK]

Hint: Use .length inside map block to get string sizes [OK]

Common Mistakes:

• Using unrelated methods like upcase or reverse
• Trying to get length without block variable
• Confusing map with each for transformation