Hashes in Ruby

Hashes are data structures that allow key-value pairs to be stored. They are a fundamental tool in Ruby to work with data in an organized and efficient way.

Creating and accessing values: Link to heading

They can be created using curly braces and separating pairs with commas.
The size of the hash can be obtained with the size method.
Values can be accessed by their key.

Examples: Link to heading

capitals = { }

capitals.class # => Hash

capitals = { "Spain" => "Madrid" }

# Add value
capitals["Uruguay"] = "Montevideo"

puts capitals # => { "Spain" => "Madrid", "Uruguay" => "Montevideo" }

# Access a specific value
capitals["Spain"] # => "Madrid"

capitals.size # => 2

capitals.empty? # => false

capitals.has_value? "Spain" # => false

capitals.has_key? "Spain" # => true

# Invert the hash (convert values to keys)
capitals.invert # => { "Madrid" => "Spain", "Montevideo" => "Uruguay" }

# Mix two hashes
capitals.merge({"Brazil" => "Brasilia"}) # => {"Spain" => "Madrid", "Uruguay" => "Montevideo", "Brazil" => "Brasilia"}

# Transform the values
capitals.transform_values { |x| x.downcase } # => {"spain" => "madrid", "uruguay" => "montevideo"}

# Print the content of the hash
puts capitals.map { |k, v| "The capital of #{k} is #{v}" } # The capital of Spain is Madrid, The capital of Uruguay is Montevideo

# Convert an array to a hash
[["hello", 13], ["world", 14]].to_h # => {"hello" => 13, "world" => 14}

Useful methods: Link to heading

each: Loops through the hash and executes a block of code for each key-value pair.
select: Filters the hash key-value pairs and returns a new hash with those that meet a condition.
keys: Obtains an array with the hash keys.
values: Obtains an array with the hash values.

Example: Link to heading

capitals.each { |k, v| puts "The capital of #{k} is #{v}" } # The capital of Spain is Madrid, The capital of Uruguay is Montevideo

capitals.select { |k, v| v.length > 8 } # => {"Uruguay" => "Montevideo"}

capitals.keys # => ["Spain", "Uruguay"]

capitals.values # => ["Madrid", "Montevideo"]

Hashes are a powerful tool for storing and organizing data in Ruby. Their flexibility and efficiency make them a fundamental part of the language.

Keep learning about hashes to take full advantage of Ruby!