How is a dictionary different from an array in Swift?

In Swift, a dictionary and an array are two distinct data structures with different characteristics and purposes. Here are the main differences between a dictionary and an array:

1. Structure:
- Array: An array is an ordered collection of elements. Elements are stored in sequential order and accessed by their index, which starts from 0.
- Dictionary: A dictionary is an unordered collection of key-value pairs. Elements are stored with a unique key, and values are accessed by their corresponding keys. The order of elements in a dictionary is not guaranteed.

2. Accessing Elements:
- Array: Elements in an array are accessed by their index. For example, `myArray[0]` retrieves the element at index 0.
- Dictionary: Elements in a dictionary are accessed by their keys. For example, `myDictionary[“key”]` retrieves the value associated with the key “key”.

3. Data Storage:
- Array: An array stores a collection of elements of the same type. Elements in an array are typically accessed in a sequential manner.
- Dictionary: A dictionary stores key-value pairs, where each key must be unique within the dictionary. Keys can be of any hashable type, and values can be of any type.

4. Order:
- Array: Elements in an array are ordered and maintain the sequence in which they are inserted. The order is preserved unless explicitly modified.
- Dictionary: Elements in a dictionary are not ordered. The order of elements may change when modifying or adding elements, and there is no inherent order based on insertion.

5. Common Use Cases:
- Array: Arrays are commonly used when you need to store and access a collection of elements in a specific order, such as a list of names or a sequence of values.
- Dictionary: Dictionaries are useful when you need to associate values with unique keys. They are commonly used to represent mappings, lookups, or to store data in a key-value format.

It’s important to choose the appropriate data structure based on your specific needs. If you have a collection of elements without the need for key-value associations, an array is usually the better choice. On the other hand, if you require key-based access or need to associate values with unique keys, a dictionary is more suitable.