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Ruby Fundamentals: Hashes

Ruby Fundamentals: Hashes

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phares muhambi
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3 min read

Hashes are basically like JavaScript objects. They are composed of key/value pairs and each key points to a specific value. For example;

a_hash = { name: "John", age: "20" }
a_hash[:age]
# => "20"

To access data from the hash above, bracket notation is used and the symbol for the key being accessed is passed in. It can also be used to assign a new value to a key: 

a_hash[:age] = 25
a_hash
# => {:name=>"John", :age=>25}

Enumerable

Enumerable is a method that "enumerates" (goes one by one) over every element of a collection. Enumerables include:

  • Map
  • Times
  • Each
  • Collect
  • Find
  • Sum

Common Hash Methods

While bracket notation is used to access values in a hash, they can also be deleted using the delete method by passing in a key: 

snacks = { crisps: true, flavor1: "salted", flavor2: "barbecue" }
snacks.delete(:flavor2)
snacks
# => {:crisps=>true, :flavor1=>"salted"}

It also has methods of accessing an array of the keys and an array of the values: 

snacks.keys
# => [:crisps, :flavor1]
snacks.values
# => [true, "salted"]

It uses the empty method to check if there are no key-value pairs defined on the hash: 

snacks.empty?
# => false
{}.empty?
# => true

It uses the merge method to join together multiple hashes: 

more_flavors = { flavor2: "barbecue", flavor3: "salt and vinegar" }

snacks.merge(more_flavors)

# => {:crisps=>true, :flavor1=>"salted", :flavor2=>"barbecue", :flavor3=>"salt and vinegar"}

Enumerables:Common Methods

Include :

  • each
  • map/collect
  • filter/ #select/#find_all
  • find / #detect
  • sort

    EachMethod

Used To access each element of the array, but not interested in returning a new array Has the same functionality as foreach which is used in JS

new_array = ["this", "is", "Ruby"].each do |str|
  puts str.upcase
end

"THIS"
 "IS"
 "RUBY"

MapMethod

Uses To access every element of an array, calculates the new value and returns the new values with the same length as the original array.

[1, 2, 3].map { |num| num * 2 }
# => [2, 4, 6]

users = [{ name: "Duane", phone: "555-555-5555"}, { name: "Liza", phone: "555-555-5556" }]
users.map do |user|
  "Name: #{user[:name]} | Phone: #{user[:phone]}"
end
# => ["Name: Duane | Phone: 555-555-5555", "Name: Liza | Phone: 555-555-5556"]

[1, 2, 3].collect { |num| num * 2 }
# => [2, 4, 6]

FilterMethod

Uses To access every element of an array,check is it matches some condition, then returns a new array of all values that match Alias #select , #find_all

[1, 2, 3, 4, 5].filter { |num| num.even? }
# => [2, 4]
[1, 2, 3, 4, 5].filter { |num| num.odd? }
=> [1, 3, 5]

SortMethod

Uses Returns a new array where all elements have been sorted based on the criteria.

nums = [1, 5, 3]
sorted_nums = nums.sort
sorted_nums
# => [1, 3, 5]

find

Uses To access every element of an array, checks if it matches some criteria, then returns the first element that matches .

[1, 2, 3, 4, 5].find { |num| num.even? }
# => 2
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