Great job! In this lesson, we went over the following concepts:

• A dictionary is an unordered collection of key-value pairs.

• A key is a unique identifier used to create, update, remove, or access an associated value.

• We can create populated dictionaries using dictionary literals:

  var dictionaryName = [Key1: Value1, Key2: Value2]

• An empty dictionary contains no key-values pairs. There are two methods of initializing an empty dictionary:

  // Initializer Syntax:
  var emptyInitializer = [KeyType: ValueType]()
  // Dictionary Literal Syntax:
  var emptyLiteral: [KeyType: ValueType] = [:]

• We can add elements to a dictionary using subscript syntax:

  dictionaryName[NewKey] = NewValue

• We can remove dictionary elements using .removeValue() or by setting a key value to nil.

  dictionaryName.removeValue(forKey: Key)
  dictionaryName[Key] = nil

• We can remove all the values from a dictionary with .removeAll().

• We can update the value of a key-value pair using subscript syntax or .updateValue():

  dictionaryName[Key] = NewValue
  dictionaryName.updateValue(NewValue, forKey: Key)

• The .isEmpty property returns a boolean that equals true if a dictionary is empty.

• The .count property returns the number of elements contained within a dictionary.

• We can access a value using its key:

  dictionaryName[Key]

• We can use for-in loops to iterate through the content of a dictionary:

  for (KeyHolder, ValueHolder) in dictionaryName {
  // Add body
  }

• We can use the .keys property to access only the keys of a dictionary.

• We can use the .values property to access only the values of a dictionary.