What are hashes? 

• Like an array, but the index can be anything:
• integers, strings, symbols, or even objects
• Instead of array[1] = "fun" we have hash["ruby"] = "fun"
• Example:
• StudentNumbers = { "WDI4" => 9, "WDI5" => 15 }

An analogy

Array 

Hash

Grocery shopping

Why are they cool? 

• Human readable: animals[1] vs animals["cats"]
• One of the most common data structures you'll encounter
• Key-value logic is everywhere, even in NoSQL databases

When will you use them?

• Does your data need a label?
• Do you need fast lookups? 
• Are you working with JSON? 
• require 'json' then hash.to_json

Using hashes:

code-along

Further reading

• http://ruby-doc.org/core-2.2.0/Hash.html
• https://launchschool.com/books/ruby/read/hashes
• https://en.wikipedia.org/wiki/Associative_array