Zip for combining arrays in Ruby - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Ruby code using zip?

Consider the following Ruby code that uses zip to combine arrays. What will it print?

Ruby

a = [1, 2, 3]
b = ['a', 'b', 'c']
result = a.zip(b)
puts result.inspect

A [[1, "a"], [2, "b"]]

B [[1, "a"], [2, "b"], [3, "c"]]

C [[1, "a"], [2, "b"], [3, nil]]

D [[1, 2, 3], ["a", "b", "c"]]

💡 Hint

Remember that zip pairs elements by their index from each array.

The zip method pairs elements from each array by their index. Since both arrays have 3 elements, the result is an array of 3 pairs.

❓ Predict Output

intermediate

What happens when arrays of different lengths are zipped?

Look at this Ruby code where arrays of different lengths are zipped. What is the output?

Ruby

x = [10, 20]
y = ['x', 'y', 'z']
result = x.zip(y)
puts result.inspect

A [[10, "x"], [20, "y"]]

B [[10, "x"], [20, "y"], [nil, "z"]]

C [[10, "x"], [20, "y"], [20, "z"]]

D [[10, "x"], [20, "y"], [nil, nil]]

💡 Hint

The length of the resulting array matches the receiver array's length.

The zip method returns an array with the same length as the first array. Extra elements in the second array are ignored.

🔧 Debug

advanced

Why does this zip code raise an error?

Examine this Ruby code snippet. It raises an error. What is the cause?

Ruby

a = [1, 2, 3]
b = nil
result = a.zip(b)
puts result.inspect

A ArgumentError because <code>zip</code> expects arrays only

B TypeError because <code>nil</code> cannot be converted to array

C NoMethodError because <code>nil</code> does not respond to <code>to_ary</code>

D SyntaxError due to wrong method call

💡 Hint

Think about what zip does internally with its arguments.

The zip method tries to convert arguments to arrays using to_ary. Since nil does not have this method, it raises NoMethodError.

🧠 Conceptual

advanced

How does zip behave with a block?

What is the output of this Ruby code that uses zip with a block?

Ruby

a = [1, 2, 3]
b = ['x', 'y', 'z']
a.zip(b) { |num, char| puts "#{num}-#{char}" }

A

Prints:
1-x
2-y
3-z
and returns nil

B

Prints:
[1, "x"]
[2, "y"]
[3, "z"]
and returns the zipped array

C Prints nothing and returns the zipped array

D

Prints:
1-x
2-y
3-z
and returns the zipped array

💡 Hint

Remember what zip returns when given a block.

When zip is called with a block, it yields each combined array to the block and returns nil.

🚀 Application

expert

How many pairs are in the zipped array?

Given these arrays, how many pairs will the zipped array contain?

Ruby

arr1 = [5, 10, 15, 20]
arr2 = ['a', 'b']
arr3 = [:x, :y, :z]
result = arr1.zip(arr2, arr3)

A 1 pair

B 3 pairs

C 2 pairs

D 4 pairs

💡 Hint

The number of pairs equals the length of the first array.

The zip method returns an array with the same length as the first array, pairing elements from all given arrays by index.

Practice

1. What does the Ruby method zip do when used with two arrays?

easy

A. Concatenates the two arrays into one long array.

B. Combines elements from both arrays into pairs based on their positions.

C. Removes duplicate elements from both arrays.

D. Sorts both arrays in ascending order.

Solution

1. Step 1: Understand the purpose of zip

   The zip method pairs elements from arrays by their index positions.

2. Step 2: Compare with other array operations

   Unlike sorting or concatenation, zip creates pairs, not a sorted or merged list.

3. Final Answer:

   Combines elements from both arrays into pairs based on their positions. -> Option B

4. Quick Check:

   Zip pairs elements by position = D [OK]

Hint: Zip pairs elements by index from arrays [OK]

Common Mistakes:

• Thinking zip sorts arrays
• Assuming zip concatenates arrays
• Confusing zip with removing duplicates

2. Which of the following is the correct syntax to zip two arrays a and b in Ruby?

easy

A. a.zip(b)

B. zip(a, b)

C. a.zip = b

D. zip a, b

Solution

1. Step 1: Recall Ruby method call syntax

   In Ruby, methods are called on objects with dot notation, so a.zip(b) is correct.

2. Step 2: Identify incorrect syntax

   The other options do not follow Ruby's method call syntax and will cause errors.

3. Final Answer:

   a.zip(b) -> Option A

4. Quick Check:

   Method call with dot and parentheses = A [OK]

Hint: Use dot notation: array.zip(other_array) [OK]

Common Mistakes:

• Using zip as a standalone function
• Assigning zip like a variable
• Omitting parentheses incorrectly

3. What is the output of the following Ruby code?

a = [1, 2, 3]
b = ['a', 'b', 'c']
result = a.zip(b)
puts result.inspect

medium

A. [[1, 2, 3], ['a', 'b', 'c']]

B. [1, 'a', 2, 'b', 3, 'c']

C. [[1, 'a'], [2, 'b'], [3, nil]]

D. [[1, 'a'], [2, 'b'], [3, 'c']]

Solution

1. Step 1: Understand zip pairing

   The method pairs elements by index: 1 with 'a', 2 with 'b', 3 with 'c'.

2. Step 2: Check output format

   The result is an array of arrays, each inner array holding one pair.

3. Final Answer:

   [[1, 'a'], [2, 'b'], [3, 'c']] -> Option D

4. Quick Check:

   Zip pairs elements by index = B [OK]

Hint: Zip pairs elements index-wise into nested arrays [OK]

Common Mistakes:

• Expecting flat array instead of nested arrays
• Confusing zip with concatenation
• Misunderstanding nil insertion

4. The following Ruby code is intended to zip two arrays but raises an error. What is the problem?

a = [1, 2]
b = ["x", "y", "z"]
result = a.zip *b
puts result.inspect

medium

A. Using double quotes instead of single quotes causes error.

B. Arrays have different lengths, causing an error.

C. Missing parentheses around argument in zip *b call.

D. The variable result is not defined before use.

Solution

1. Step 1: Check method call syntax

   In Ruby, calling zip without parentheses is allowed only if no ambiguity exists, but here parentheses are recommended.

2. Step 2: Confirm array length and variable usage

   Different lengths do not cause errors; zip fills missing with nil. Variables are defined correctly.

3. Final Answer:

   Missing parentheses around argument in zip *b call. -> Option C

4. Quick Check:

   Use parentheses for method arguments to avoid errors = C [OK]

Hint: Use parentheses with method arguments to avoid syntax errors [OK]

Common Mistakes:

• Assuming different lengths cause errors
• Ignoring parentheses in method calls
• Confusing string quote types with errors

5. Given two arrays names = ["Alice", "Bob", "Carol"] and scores = [85, 92], which Ruby code correctly zips them and replaces missing scores with 0?

hard

A. All of the above

B. names.zip(scores).map { |name, score| [name, score ? score : 0] }

C. names.zip(scores).map { |name, score| [name, score.nil? ? 0 : score] }

D. names.zip(scores).map { |name, score| [name, score || 0] }

Solution

1. Step 1: Understand zip with unequal lengths

   Zipping names and scores pairs elements; missing scores become nil.

2. Step 2: Replace nil with 0 using different Ruby idioms

   All options use valid Ruby ways to replace nil or falsey values with 0.

3. Step 3: Confirm all options work correctly

   Each option correctly maps pairs and replaces missing scores with 0.

4. Final Answer:

   All of the above -> Option A

5. Quick Check:

   All methods replace nil with 0 after zip = A [OK]

Hint: Use map with nil check to replace missing values after zip [OK]

Common Mistakes:

• Ignoring nil values after zip
• Using incorrect nil checks
• Assuming zip fills missing with 0 automatically