Symbols and Hashes Intro

Intro to Symbols and Hashes

Transcript

1. Strings and Hashes
2. What is it ? • Symbol is something used to represent a string. • A more memory efficient and descriptive way to do things.
3. How does it look ? Colon followed by a non-quoted string - :symbol Or Colon followed by quoted string - :'this is another symbol'
4. Assigning stuff to symbols • :my_symbol = “foo_bar” - wrong • my_symbol = :foo_bar – right • attr_accessor :foo_bar • my_symbol = :foo_bar.to_s
5. Symbols are immutable
6. hash • Data structure – collection of key value pairs • Indexing via keys of object _type • Randomly ordered
7. What does it look like ? • animals = Hash.new • animals["dog"] = "bark" • pry(main)> animals => {"dog"=>"bark", "cat"=>"purr"}
8. • Iterating over an array • animal_farm.each do |a| puts a end • Iterating over a hash • animals.each do |k,v| puts “#{k} and #{v} end
9. exercise • Create a hash to represent currencies eg USA => usd , UK => gbp, JAPAN => yen • Display all the currencies • Replace all the name of countries with their short codes eg US -> US, JAPAN –> JP, UK -> UK
10. Solution • currencies = { “USA” => “usd” , “UK” => “gbp”, “JAPAN” => “yen” } • new_currencies = {"US" => "usd", "UK" => "gbp", “JP” => “yen”} • Hash[currencies.map {|k, v| [new_currencies[k], v] }]