August 4, 2020

How to sort a dictionary by value with Swift

How to sort a dictionary by value with Swift

Every now and then you might need to sort a dictionary by value, luckily, dictionary comes with a sorted method built in.

I am going to use the following dictionary as an example:

let dictionary = [
    "a": "A",
    "b": "B",
    "c": "C",
    "d": "D",
    "e": "E",
]

Let's sort the dictionary in descending order based on the values:

let sortedOne = dictionary.sorted { (first, second) -> Bool in
    return first.value > second.value
}

As you can see, the sorted method takes a closure as an argument. This closure takes two arguments and returns a bool value. Each argument is a tuple that contains two values, key and value. This is what allows us to access the value of the either the key or value in the dictionary. Because we want to sort by value, we will use the value element.

If we print sortedOne we will see the following:

[(key: "e", value: "E"), (key: "d", value: "D"), (key: "c", value: "C"), (key: "b", value: "B"), (key: "a", value: "A")]

If you want to sort by ascending order you can use < instead of >.

There is a shorter way of sorting by dictionary value. It is basically the same as the previous example, but it is a shorthand version as you can see below:

let sortedTwo = dictionary.sorted {
    return $0.value > $1.value
}

Instead of naming the arguments in the closure, we can access them by using $0 and $1. In this example, $0 is the same as first and $1 is the same as second from the first example, sortedOne.

The tuple arguments have named elements, key and value, but, if you wanted to, you could access the elements by position. So instead of $0.value you could do $0.1, see the below modified version of sortedTwo:

let sortedTwo = dictionary.sorted {
    return $0.1 > $1.1
}

Personally I am not a fan of this as I find it difficult to read, but if you want the code to be a bit shorter or want to put it on one line, then this can help.

Conclusion

Sorting a dictionary by value is incredibly easy with the sorted method. And as a quick reminder, < will sort in ascending order and > will sort in descending order.

If you want the full source, you can find it here.