Accessing and setting values in Ruby - Mini Project: Build & Apply

Accessing and setting values

📖 Scenario: You are managing a small store's inventory using a Ruby program. You need to keep track of the quantity of different fruits available.

🎯 Goal: Build a Ruby program that creates a hash with fruit quantities, updates the quantity of one fruit, and then prints the updated quantity.

📋 What You'll Learn

Create a hash named inventory with exact keys and values

Create a variable named fruit_to_update with the exact string value

Update the quantity of the fruit in the inventory hash using the variable

Print the updated quantity of the fruit using puts

💡 Why This Matters

🌍 Real World

Managing inventory quantities in a store or warehouse is a common task. Using hashes to store and update product counts helps keep track of stock easily.

💼 Career

Many programming jobs require working with data structures like hashes or dictionaries to manage and update information efficiently.

1

Create the inventory hash

Create a hash called inventory with these exact entries: 'apple' => 10, 'banana' => 5, 'orange' => 8

Ruby

# Create the inventory hash with exact fruit quantities
# Your code here

Hint

Use curly braces {} to create a hash and separate keys and values with =>.

2

Set the fruit to update

Create a variable called fruit_to_update and set it to the string 'banana'

Ruby

inventory = { 'apple' => 10, 'banana' => 5, 'orange' => 8 }
# Create the variable fruit_to_update with value 'banana'
# Your code here

Hint

Use = to assign the string 'banana' to the variable fruit_to_update.

3

Update the quantity of the selected fruit

Increase the quantity of the fruit stored in fruit_to_update by 3 in the inventory hash

Ruby

inventory = { 'apple' => 10, 'banana' => 5, 'orange' => 8 }
fruit_to_update = 'banana'
# Increase the quantity of fruit_to_update by 3
# Your code here

Hint

Use inventory[fruit_to_update] to access the value and add 3 to it.

4

Print the updated quantity

Use puts to print the updated quantity of the fruit stored in fruit_to_update from the inventory hash

Ruby

inventory = { 'apple' => 10, 'banana' => 5, 'orange' => 8 }
fruit_to_update = 'banana'
inventory[fruit_to_update] += 3
# Print the updated quantity of fruit_to_update
# Your code here

Hint

Use puts inventory[fruit_to_update] to print the updated quantity.

Practice

1. Which of the following correctly accesses the first element of an array arr in Ruby using indexing?

easy

A. arr[1]

B. arr.first()

C. arr[0]

D. arr.get(0)

Solution

1. Step 1: Understand array indexing in Ruby

   Ruby arrays start at index 0, so the first element is at arr[0].

2. Step 2: Check each option

   arr[0] correctly accesses the first element. arr[1] accesses the second element. arr.first() is a method call that also returns the first element but is not using square brackets. arr.get(0) is invalid syntax in Ruby.

3. Final Answer:

   arr[0] -> Option C

4. Quick Check:

   First element index = 0 [OK]

Hint: Remember: array indexes start at zero in Ruby [OK]

Common Mistakes:

• Using index 1 for first element
• Using method calls instead of brackets
• Trying to use non-existent methods like get()

2. Which syntax correctly sets the value of key :name to "Alice" in a Ruby hash person?

easy

A. person[:name] == "Alice"

B. person.name = "Alice"

C. person["name"] = Alice

D. person[:name] = "Alice"

Solution

1. Step 1: Understand hash key assignment syntax

   To set a value in a hash, use square brackets with the key and assign with =.

2. Step 2: Analyze each option

   person[:name] = "Alice" correctly sets the key :name. person.name = "Alice" is invalid for hashes. person["name"] = Alice misses quotes around Alice, causing error. person[:name] == "Alice" is a comparison, not assignment.

3. Final Answer:

   person[:name] = "Alice" -> Option D

4. Quick Check:

   Use brackets and = for hash assignment [OK]

Hint: Use brackets and = to set hash values [OK]

Common Mistakes:

• Using dot notation for hashes
• Forgetting quotes around string values
• Using == instead of = for assignment

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

arr = [10, 20, 30]
arr[1] = 50
puts arr.inspect

medium

A. [10, 50, 30]

B. [10, 20, 30]

C. [50, 20, 30]

D. Error

Solution

1. Step 1: Understand array element assignment

   Assigning arr[1] = 50 changes the element at index 1 (second element) to 50.

2. Step 2: Check the array after assignment

   Original array is [10, 20, 30]. After assignment, it becomes [10, 50, 30].

3. Final Answer:

   [10, 50, 30] -> Option A

4. Quick Check:

   Index 1 value changed to 50 [OK]

Hint: Index 1 means second element in array [OK]

Common Mistakes:

• Thinking index 1 is first element
• Expecting original array unchanged
• Confusing assignment with comparison

4. Identify the error in this Ruby code that tries to set a hash value:

person = {name: "Bob"}
person.name = "Charlie"

medium

A. Missing quotes around "Charlie"

B. Using dot notation to set hash value causes error

C. Hash keys must be strings, not symbols

D. person variable is not defined

Solution

1. Step 1: Understand hash value setting syntax

   Hashes use square brackets with keys to access or set values, not dot notation.

2. Step 2: Analyze the code

   person.name = "Charlie" tries to use dot notation, which is invalid for hashes and causes an error.

3. Final Answer:

   Using dot notation to set hash value causes error -> Option B

4. Quick Check:

   Use brackets, not dot, for hash assignment [OK]

Hint: Use brackets, not dot, to set hash values [OK]

Common Mistakes:

• Using dot notation for hashes
• Confusing symbols and strings for keys
• Assuming variable is undefined

5. Given the nested hash data = {user: {name: "Eve", age: 28}}, how do you change the user's age to 30?

hard

A. data[:user][:age] = 30

B. data[:user.age] = 30

C. data.user[:age] = 30

D. data[:user][age] = 30

Solution

1. Step 1: Access nested hash keys with brackets

   To access nested values, use square brackets for each key: data[:user][:age].

2. Step 2: Assign new value to nested key

   Set data[:user][:age] = 30 to update the age.

3. Final Answer:

   data[:user][:age] = 30 -> Option A

4. Quick Check:

   Use chained brackets for nested hashes [OK]

Hint: Chain brackets for nested hash keys [OK]

Common Mistakes:

• Using dot notation for hashes
• Missing quotes or symbols for keys
• Using undefined variables as keys