Array modification (push, pop, shift, unshift) in Ruby - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the push method do in a Ruby array?

The push method adds one or more elements to the end of an array.

beginner

How does the pop method modify an array?

The pop method removes the last element from an array and returns it.

beginner

What is the difference between shift and pop in Ruby arrays?

shift removes the first element of the array, while pop removes the last element.

beginner

What does the unshift method do in a Ruby array?

The unshift method adds one or more elements to the beginning of an array.

beginner

If you have arr = [1, 2, 3] and you run arr.unshift(0), what will arr be?

The array will be [0, 1, 2, 3] because unshift adds the element 0 to the start.

Which method removes the last element from a Ruby array?

A pop

B shift

C push

D unshift

The pop method removes and returns the last element of the array.

What does arr.push(4) do if arr = [1, 2, 3]?

A Adds 4 to the beginning of the array

B Removes the first element

C Adds 4 to the end of the array

D Removes the last element

push adds the element to the end of the array.

Which method removes the first element from a Ruby array?

A shift

B unshift

C push

D pop

shift removes and returns the first element of the array.

What will arr.unshift(0) do to arr = [1, 2, 3]?

A Remove the first element

B Remove the last element

C Add 0 to the end

D Add 0 to the beginning

unshift adds elements to the start of the array.

If you want to add an element to the end of an array, which method should you use?

A pop

B push

C shift

D unshift

Use push to add elements to the end of an array.

Explain how the methods push, pop, shift, and unshift modify a Ruby array.

Think about adding or removing elements from the start or end of the array.

Describe a real-life situation where you might use shift and pop on an array.

Imagine a line of people or a stack of objects.

Practice

1. Which Ruby array method adds an element to the end of the array?

easy

A. shift

B. pop

C. push

D. unshift

Solution

1. Step 1: Understand the purpose of push

   The push method adds an element to the end of an array.

2. Step 2: Compare with other methods

   pop removes the last element, shift removes the first, and unshift adds to the front.

3. Final Answer:

   push -> Option C

4. Quick Check:

   push adds to end [OK]

Hint: Remember: push = add end, unshift = add front [OK]

Common Mistakes:

• Confusing push with pop
• Mixing shift and unshift
• Thinking pop adds elements

2. Which of the following is the correct syntax to remove the first element from an array arr in Ruby?

easy

A. arr.shift()

B. arr.pop()

C. arr.unshift()

D. arr.push()

Solution

1. Step 1: Identify method to remove first element

   The shift method removes and returns the first element of an array.

2. Step 2: Check syntax correctness

   Calling arr.shift() correctly removes the first element.

3. Final Answer:

   arr.shift() -> Option A

4. Quick Check:

   shift removes first element [OK]

Hint: shift removes first, pop removes last [OK]

Common Mistakes:

• Using pop to remove first element
• Calling unshift to remove elements
• Forgetting parentheses

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

arr = [1, 2, 3]
arr.push(4)
arr.shift
p arr

medium

A. [1, 2, 3]

B. [1, 2, 3, 4]

C. [4, 1, 2, 3]

D. [2, 3, 4]

Solution

1. Step 1: Execute push(4) on array

   Adding 4 to the end changes array from [1, 2, 3] to [1, 2, 3, 4].

2. Step 2: Execute shift to remove first element

   Removing first element (1) results in [2, 3, 4].

3. Final Answer:

   [2, 3, 4] -> Option D

4. Quick Check:

   push adds end, shift removes front = [2, 3, 4] [OK]

Hint: push adds end, shift removes front, watch order [OK]

Common Mistakes:

• Ignoring shift effect
• Thinking push adds front
• Confusing pop with shift

4. The following Ruby code is intended to add 0 to the front of the array nums and then remove the last element. What is the error?

nums = [1, 2, 3]
nums.unshift(0)
nums.pop()

medium

A. No error; code works correctly

B. pop() should be called before unshift()

C. unshift() does not add elements to array

D. pop() removes the first element, not the last

Solution

1. Step 1: Understand unshift(0) effect

   This adds 0 to the front, changing [1, 2, 3] to [0, 1, 2, 3].

2. Step 2: Understand pop() effect

   This removes the last element (3), resulting in [0, 1, 2].

3. Final Answer:

   No error; code works correctly -> Option A

4. Quick Check:

   unshift adds front, pop removes last = correct [OK]

Hint: unshift adds front, pop removes last, order matters [OK]

Common Mistakes:

• Thinking pop removes first element
• Believing unshift does not add
• Swapping order of operations unnecessarily

5. Given the array data = [10, 20, 30], which sequence of method calls will result in [5, 10, 20]?

hard

A. data.push(5).shift()

B. data.unshift(5).pop()

C. data.shift().unshift(5)

D. data.pop().unshift(5)

Solution

1. Step 1: Apply unshift(5) to add 5 at front

   Array changes from [10, 20, 30] to [5, 10, 20, 30].

2. Step 2: Apply pop() to remove last element

   Removing last element (30) results in [5, 10, 20].

3. Final Answer:

   data.unshift(5).pop() -> Option B

4. Quick Check:

   unshift adds front, pop removes last = [5, 10, 20] [OK]

Hint: Add front with unshift, then remove last with pop [OK]

Common Mistakes:

• Using push instead of unshift
• Removing first element instead of last
• Chaining methods incorrectly