Modifying Hashes

Part of the Fundamentals section of Coddy's Ruby journey — lesson 75 of 88.

Hashes aren't static once created. You can add new key-value pairs, update existing values, and remove entries as your program runs.

To add a new pair or update an existing value, assign to the key using square brackets:

person = {"name" => "Alice", "age" => 25}

person["city"] = "Paris"      # Adds a new key-value pair
person["age"] = 26            # Updates existing value

puts person  # Outputs: {"name"=>"Alice", "age"=>26, "city"=>"Paris"}

If the key exists, the value gets replaced. If it doesn't exist, a new pair is added to the hash.

To remove a key-value pair, use the delete method with the key you want to remove:

person = {"name" => "Alice", "age" => 25, "city" => "Paris"}

person.delete("city")

puts person  # Outputs: {"name"=>"Alice", "age"=>25}

The delete method returns the value that was removed, which can be useful if you need to use it:

person = {"name" => "Alice", "age" => 25}

removed_age = person.delete("age")

puts removed_age  # Outputs: 25

If you try to delete a key that doesn't exist, Ruby simply returns nil without raising an error.

Challenge

Easy

Read four lines of input:

A student name (string)
An initial grade (integer)
A new grade to update (integer)
A new key-value pair in the format key:value (e.g., subject:Math)

Create a hash called student with the following initial key-value pairs:

"name" mapped to the student name
"grade" mapped to the initial grade (as an integer)

Then perform these modifications:

Update the "grade" key with the new grade value
Add a new key-value pair using the key and value from the fourth input (the value should remain a string)
Delete the "name" key from the hash and store the removed value

Print the removed name on the first line, then print the final hash on the second line.

For example, if the inputs are Alice, 85, 92, and subject:Math, the output should be:

Alice
{"grade"=>92, "subject"=>"Math"}

If the inputs are Bob, 70, 75, and status:passing, the output should be:

Bob
{"grade"=>75, "status"=>"passing"}

If the inputs are Charlie, 100, 95, and note:excellent, the output should be:

Charlie
{"grade"=>95, "note"=>"excellent"}

Cheat sheet

To add a new key-value pair or update an existing value in a hash, use square brackets:

person = {"name" => "Alice", "age" => 25}

person["city"] = "Paris"      # Adds a new key-value pair
person["age"] = 26            # Updates existing value

puts person  # Outputs: {"name"=>"Alice", "age"=>26, "city"=>"Paris"}

If the key exists, the value gets replaced. If it doesn't exist, a new pair is added.

To remove a key-value pair, use the delete method:

person = {"name" => "Alice", "age" => 25, "city" => "Paris"}

person.delete("city")

puts person  # Outputs: {"name"=>"Alice", "age"=>25}

The delete method returns the removed value:

removed_age = person.delete("age")

puts removed_age  # Outputs: 25

If you try to delete a key that doesn't exist, Ruby returns nil without raising an error.

Try it yourself

# Read input
name = gets.chomp
initial_grade = gets.to_i
new_grade = gets.to_i
key_value_pair = gets.chomp

# TODO: Write your code below
# 1. Create a hash called 'student' with "name" and "grade" keys
# 2. Update the "grade" key with the new grade value
# 3. Parse the key_value_pair and add it to the hash
# 4. Delete the "name" key and store the removed value

# Output the removed name
puts removed_name
# Output the final hash
puts student