How to Use Hashes in Ruby on Rails

09/20/2021

Contents

In this article, you will learn how to use hashes in Ruby on Rails.

Using hashes

In Ruby on Rails, hashes are a commonly used data structure for storing key-value pairs. They are similar to arrays, but instead of indexing elements by integers, they use keys to retrieve values.

Here’s a quick guide on how to use hashes in Ruby on Rails:

Creating a hash

You can create a new hash using curly braces {} or the Hash.new method. Here are some examples:

# Using curly braces
my_hash = { "key1" => "value1", "key2" => "value2" }

# Using the Hash.new method
my_hash = Hash.new
my_hash["key1"] = "value1"
my_hash["key2"] = "value2"

Accessing values

You can access a value in a hash by its key using square brackets [] or the Hash#fetch method. Here are some examples:

# Using square brackets
my_hash["key1"] #=> "value1"

# Using the fetch method
my_hash.fetch("key2") #=> "value2"

Note: If you try to access a key that doesn’t exist in the hash, you will get a nil value. You can also set a default value to be returned if the key doesn’t exist, like this:

my_hash.fetch("key3", "default_value") #=> "default_value"

Iterating over a hash

You can iterate over a hash using the Hash#each method, which yields each key-value pair to a block. Here’s an example:

my_hash.each do |key, value|
  puts "#{key}: #{value}"
end

This will output:

key1: value1
key2: value2

Modifying a hash

You can modify a hash by assigning a new value to an existing key or adding a new key-value pair. Here are some examples:

# Assigning a new value to an existing key
my_hash["key1"] = "new_value"
my_hash #=> {"key1"=>"new_value", "key2"=>"value2"}

# Adding a new key-value pair
my_hash["key3"] = "value3"
my_hash #=> {"key1"=>"new_value", "key2"=>"value2", "key3"=>"value3"}
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