Code Along: Manipulating Nested Hashes

Objectives

1. Iterate through a nested hash
2. Modify the correct element in a nested hash

Why Nested Hashes Matter

So much of what we do in programming involves storing data in hashes. Often the hashes that we will encounter will have more than one level. As we get into the web, this will become abundantly clear. To build programs in the future, we'll absolutely need to get comfortable working with hashes. Let's get started!

Code Along Exercise

Fork and clone this lab. You'll be coding your solution in lib/contacts.rb. You'll be manipulating the following Hash:

contacts = {
  "Jon Snow" => {
    name: "Jon",
    email: "jon_snow@thewall.we",
    favorite_ice_cream_flavors: ["chocolate", "vanilla"]
  },
  "Freddy Mercury" => {
    name: "Freddy",
    email: "freddy@mercury.com",
    favorite_ice_cream_flavors: ["strawberry", "cookie dough", "mint chip"]
  }
}

Your good buddy Freddy Mercury has recently developed a strawberry allergy! You need to delete "strawberry" from his list of favorite ice cream flavors in the remove_strawberry method.

Iterate over the contacts hash and when you reach the key :favorite_ice_cream_flavors, remove "strawberry" from the Array of Freddy's favorite ice cream flavors.

There are at least two ways you can accomplish this, and for this codealong, we'll work with the second way.

1. You can directly iterate over the hash that is the value of the "Freddy Mercury" key by calling an enumerator method in contacts["Freddy Mercury"].

2. You can set a conditional to iterate through the hash for Freddy Mercury only and when you reach the appropriate level, check to see if the key == ("is equal to") :favorite_ice_cream_flavors. If it does, check to see if that array contains "strawberry". If it does, then delete it from the Array.

Step 1: Iterate over the first level

Inside the remove_strawberry method, let's take our first dive into the contacts Hash. Then we'll use binding.pry to see where we are.

We are going to first iterate over the top level of the Hash where the keys should be the person and the values should be a Hash of details about the person.

Note on variable naming: This process will be remarkably easier if you name your variables to accurately reflect the data they represent. For now, when the value we're iterating over is another hash, we will explicitly add a _hash to the end of the variable name (E.G. contact_details_hash below).

contacts.each do |person, contact_details_hash|
  binding.pry
end

In the terminal, let's hit the pry by running learn, and check that our defined variables (person and contact_details_hash) match our expectations.

> person
=> "Jon Snow"

> contact_details_hash
=> {:name=>"Jon", :email=>"jon_snow@thewall.we", :favorite_ice_cream_flavors=>["chocolate", "vanilla"]}

Excellent! They do!

Type exit while in pry to continue (a second pry will trigger since we have two contacts). Running learn will also display a test, which we haven't passed just yet.

You can also run ruby lib/contacts.rb in the terminal - instead of displaying the the test results, this will reach the binding.pry.

Step 2. Iterate over the second level

contacts.each do |person, contact_details_hash|
  if person == "Freddy Mercury"
    contact_details_hash.each do |attribute, data|
      binding.pry
    end
  end
end

Again, let's jump into our binding.pry using learn. You should see:

> attribute
=> :name

> data
=> "Jon"

Step 3. Locate the element we're looking for

contacts.each do |person, contact_details_hash|
  if person == "Freddy Mercury"
    contact_details_hash.each do |attribute, data|
      if attribute == :favorite_ice_cream_flavors
        binding.pry
      end
    end
  end
end

What is data when we hit the binding? If it's unclear, let's go into our binding.

Step 4. Update the hash

Lastly, we will use delete_if to iterate through the ice cream array and remove any element that matches "strawberry". delete_if will iterate through the hash and delete the key/value pair if the block returns true. Learn more about it in the ruby docs..

contacts.each do |person, contact_details_hash|
  if person == "Freddy Mercury"
    contact_details_hash.each do |attribute, data|
      if attribute == :favorite_ice_cream_flavors
        data.delete_if {|ice_cream| ice_cream == "strawberry"}
      end
    end
  end
end

def remove_strawberry(contacts)
  contacts.each do |person, contact_details_hash|
    if person == "Freddy Mercury"
      contact_details_hash.each do |attribute, data|
        if attribute == :favorite_ice_cream_flavors
          data.delete_if {|ice_cream| ice_cream == "strawberry"}
        end
      end
    end
  end
end

Congrats! You made it. Test that your method works by running ruby bin/contacts in the terminal. It should output the hash without strawberry ice cream. Also, be sure to run the specs to make sure they pass.

View this lesson on Learn.co