[For super beginners] The minimum knowledge you want to keep in mind with hashes and symbols

Difference between array and hash

An array is a collection of multiple pieces of information that have the same meaning, and a hash is a collection of multiple pieces of related information.

hash

variable= {Key 1=>Value 1,Key 2=>Value 2,Key 3=>Value 3}

-Since values with different meanings can be combined into one, it is used when managing multiple related values. -Has a set of "data" and the corresponding "name" as an element ・ In hash, data is called value and name is called key.

#If you use a string as the hash key
hash1 = { "name" => "nick", "age" => 30, "country" => "UK" }

symbol

・ What is used as a numerical value for the hash key ・ Although it looks like a character string, the actual content is a numerical value. ・ There are two types of writing, but the actual situation is the same for both. ・ Hash3 is the simplest and most often used

#When using a symbol as the hash key
hash2 = { :name => "nick", :age => 30, :country => "UK" }
hash3 = { name: "nick", age: 30, country: "UK" }

⚠️ Computers process numbers faster than strings Symbols are more commonly used

So far, the super basic part is clear! !! It's a good idea to get used to the hashes written with symbols, but make sure you understand them before using them. Next, I would like to explain about adding hashes and getting double hash values! If you want to absorb a little more knowledge, please see the continuation.

Add element to hash

teacher = { name: "nick"}
teacher[:age] = 30 #hash[Key to add] =value

puts teacher

#Output result
# {:name=>"nick", :age=>30}

Change hash value

teacher = { name: "nick", age: 30}
teacher[:name] = "john" #hash[The key of the value you want to change] =value

puts teacher

#Output result
# {:name=>"john", :age=>30}

Get the hash value

teacher = { name: "nick", age: 30}
puts teacher[:name] #hash[The key of the value you want to get]

#Output result
# nick

Get the value of the double hash

#Variable teacher_data → Have multiple pieces of information as hashes inside the array
#teacher_Get name data from data

teacher_data = [
  {
    teacher: {
      profile: {
        name: "nick"
      }
    }
  },
  {
    teacher: {
      profile: {
        name: "john"
      }
    }
  },
  {
    teacher: {
      profile: {
        name: "mac"
      }
    }
  }
]

teacher_data.each do |t|
  puts t[:teacher][:profile][:name]
end

#Output result
# nick
# john
# mac

[Explanation] The block argument t uses t of teacher_data. After puts, concatenate the hash [key you want to get] to the data you want to get (name in this case).

Thank you for your hard work! !! That's all for super basic knowledge about hashes and symbols! If you don't understand the basics, you'll be in trouble later, so I hope you take this opportunity to deepen your understanding. Please do not hesitate to let us know if you have any questions or concerns! Then thank you.

reference

・ Htps: // Quiita. This m / Ryosukette r / Te ms / 257d672 Eb83210b5f8dc