Sort Dictionary by Key Value

Question

let dict: [String:Int] = ["apple":5, "pear":9, "grape":1]

How do you sort the dictionary based on the Int value so that the output is:

sortedDict = ["pear":9, "apple":5, "grape":1]

Current Attempt (doesn't sort correctly):

let sortedDict = sorted(dict) { $0.1 > $1.1 } 

Answer 1

You need to sort your dictionary values, not your keys. You can create an array of tuples from your dictionary sorting it by its values as follow:

Xcode 9 • Swift 4 or Xcode 8 • Swift 3

let fruitsDict = ["apple": 5, "pear": 9, "grape": 1]
let fruitsTupleArray = fruitsDict.sorted{ $0.value > $1.value }

fruitsTupleArray // [(.0 "pear", .1 9), (.0 "apple", .1 5), (.0 "grape", .1 1)]

for (fruit,votes) in fruitsTupleArray {
    print(fruit,votes)
}

fruitsTupleArray.first?.key   // "pear"
fruitsTupleArray.first?.value   // 9

---

To sort your dictionary using your keys

let fruitsTupleArray = fruitsDict.sorted{ $0.key > $1.key }
fruitsTupleArray  // [(key "pear", value 9), (key "grape", value 1), (key "apple", value 5)]

To sort your dictionary using its keys and localized comparison:

let fruitsTupleArray = fruitsDict.sorted { $0.key.localizedCompare($1.key) == .orderedAscending  }

---

edit/update:

We can also extend Sequence protocol and implement a custom sort that takes a predicate and sort using a keypath property as long as it conforms to Comparable:

extension Sequence {
    func sorted<T: Comparable>(_ predicate: (Element) -> T, by areInIncreasingOrder: ((T,T)-> Bool) = (<)) -> [Element] {
        sorted(by: { areInIncreasingOrder(predicate($0), predicate($1)) })
    }
}

---

Usage:

let sortedFruitsAscending = fruitsDict.sorted(\.value)
print(sortedFruitsAscending)

let sortedFruitsDescending = fruitsDict.sorted(\.value, by: >)
print(sortedFruitsDescending)

---

This will print

[(key: "grape", value: 1), (key: "apple", value: 5), (key: "pear", value: 9)]

[(key: "pear", value: 9), (key: "apple", value: 5), (key: "grape", value: 1)]

---

edit/update:

For Xcode 13 or later you can use a new generic structure called KeyPathComparator:

let fruitsTupleArray = fruitsDict.sorted(using: KeyPathComparator(\.value, order: .reverse))

Answer 2

Dictionaries can't be sorted. Generally, when I need things sorted from a dictionary, I will make a separate array of my dictionary keys.

In your case, make an array of the keys, sort them by comparing their values in the dictionary.