Delete key-value pair

var bookShelf = [
  "Goodnight": "Margaret Wise Brown",
  "The BFG": "Roald Dahl",
  "Falling Up": "Shel Silverstein",
  "No, David!": "David Shannon"
]
// remove value by setting key to nil
bookShelf["The BFG"] = nil
// remove value using .removeValue()
bookShelf. removeValue(forKey: "Goodnight")
// remove all values
bookShelf. removeAll()