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How to group arrays using dictionaries

Swift version: 5.6

Paul Hudson    @twostraws   

If you have an array of items and want to group them according to some criteria, Swift has a special dictionary initializer just for you.

Here’s an example sequence we can work with:

let singers = ["Ed Sheeran", "Ariana Grande", "Taylor Swift", "Adele Adkins"]

We can now create a dictionary that groups those singers together by the length of their names:

let groupedByLength = Dictionary(grouping: singers) { $0.count }

That will put Taylor and Adele into an array under the “12” key, Ariana under 13, and Ed under 10.

Alternatively, we could group them by the first letters of each of their names:

let groupedByFirst = Dictionary(grouping: singers) { $0.first! }
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