Frequently Used Method - Hash

Hash
1. include? , has_key?
It will return true if the object passed in match the KEY in the hash.
eg: a = {:A => 200 , :B => 300}
a.include?(200) 
returns false
a.has_key?(:A)
return true

2. each { |key, value| }
It will iterate through the hash key once. Returns the original full hash.
eg: a = {:A => 200 , :B => 300}
a.each do  |key, value| 
    puts key 
    puts value 
end
# A
# 200
# B
# 300
# return {:A => 200 , :B => 300}

3. fetch
It will return the value based on the hash key inputted
eg: a = {:A => 200 , :B => 300}
a.fetch(:A)

# return 200

4. key
It will return the key based on the value passed in.
eg: a = {:A => 200 , :B => 300}
a.key(200)

# return :A