Hashes Checkpoint

_notes

##Hashes - Another type of collection

###Hashes store elements as key / value pairs

1. Keys are not restricted to exist as integers, in fact they can be any type of object, like a String or Symbol

2. Symbols are basically lightweight strings, only with a different syntax. Symbols have a : to the left of their name. So if we wanted to create a Symbol named "book", it would simply be :book

3. Symbols are very efficient objects used to retrieve values from a hash!

4. fruits[word] #=> returns "A red, yellow or green fruit."
fruits is the Hash and word is the argument passed to the get_definition method. word is also the Hash key we're looking for.

Example of a compact/readable hash:
```
def get_definition(word)
  fruits = {
            apple: "A red, yellow or green fruit.", 
            banana: "A yellow fruit.", 
            broccoli: "A green vegetable."
            }
  p fruits[word]
end
```

_output

```Bloc output - setting attributes
 User initialize can set just the name
 User initialize can set all values
 User initialize can set no values
```

```Bloc output - Iterating over a Hash
 hash_to_array returns array for short hash
 hash_to_array returns array for longer hash
```

```Bloc output - Hash Methods
 merge_us merges two hashes that are unique
 merge_us merges two hashes that are have some things in common
 my_keys returns keys for a small hash
 my_keys returns keys for a larger hash
 do_i_have? returns false if it doesn't have any of the keys
 do_i_have? returns false if one or more of the keys isn't in the hash
 do_i_have? returns false if the hash has a different number of keys than the array
 do_i_have? returns true if all keys are in the hash
 do_i_have? returns true if all keys are in the hash, regardless of order
```

_questions

1. In the "Iterating over an array exercise", why do we create a new hash as an argument?:
def hash_to_array(h = {})
  a = []
  h.each do |key, value|
    a << "#{key} is #{value}"
  end
    a
end


....you also see it here:
class User
  attr_accessor :name, :email, :bio, :age, :sex
  def initialize(config = {})
    @name = config[:name] || "n/a"
    @email = config[:email] || "n/a" 
    @bio = config[:bio] || "n/a"
    @age = config[:age] || "n/a"
    @sex = config[:sex] || "n/a"
  end
end

Hashes Checkpoint

#SETTING ATTRIBUTES

class User
  attr_accessor :name, :email, :bio, :age, :sex
  def initialize(config = {})
    @name = config[:name] || "n/a"
    @email = config[:email] || "n/a" 
    @bio = config[:bio] || "n/a"
    @age = config[:age] || "n/a"
    @sex = config[:sex] || "n/a"
  end
end

# Iterating over a Hash

def hash_to_array(h = {})
  a = []
  h.each do |key, value|
    a << "#{key} is #{value}"
  end
    a
end

# Hash Methods

def merge_us(h1, h2)
  h1.merge!(h2)
end

def my_keys(h)
  h.keys
end

def do_i_have? (hash, array_of_keys)

  if hash.keys.sort == array_of_keys.sort
    true
  else
    false
  end
end

junk

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