Swift: sort array by comparing another array

Question

I have two arrays:

@State var myInterests: [String] = ["Beer", "Food", "Dogs", "Ducks"]
@State var otherInterests: [String] = ["Ducks", "Baseball", "Beer", "Pasta"]

I need to display a list with all shared interests listed first (top of the list), and then the others after.

ForEach(interests, id: \.self) { tag in
   Text(tag)
}

The result for otherInterests should be something like:

["Ducks", "Beer", "Baseball", "Pasta"]

Is there any way of sorting the array to move the shared interests to the front of the array and the remaining ones after?

This doesn't actually have anything to do with SwiftUI. You'll get more attention/traction to your question if you just ask about it in plain Swift terms (i.e. just remove the @State, ForEach, Text). I think this is a perfect fit for your problem: stackoverflow.com/a/43056896/3141234 — Alexander
– Alexander, Commented Aug 24, 2022 at 21:25
Actually, this is an even better fit: github.com/apple/swift-algorithms/blob/main/Guides/Partition.md — Alexander
– Alexander, Commented Aug 24, 2022 at 21:45

CloudBalancing · Accepted Answer · 2022-08-24 23:16:47Z

2

As long as the order of the subitems is not that important (you can sort each sublist to make sure consistent output) - a simple solution can be to use sets here!

Something like this

let myInterests: [String] = ["Beer", "Food", "Dogs", "Ducks"]
let otherInterests: [String] = ["Ducks", "Baseball", "Beer", "Pasta"]
// This will result only in the shared interests between my and other
let sharedInterests = Set(myInterests).intersection(Set(otherInterests))
// This will result in only the not shared interests
let resetOfOtherInterest = Set(otherInterests).subtracting((Set(sharedInterests)))
// Here we combine the two (which are disjoint!)
let newOtherInterest = Array(sharedInterests) + Array(resetOfOtherInterest)

print(newOtherInterest)

newOtherInterest = ["Ducks", "Beer", "Baseball", "Pasta"]

edited Aug 24, 2022 at 23:16

answered Aug 24, 2022 at 21:22

CloudBalancing

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5 Comments

Alexander Over a year ago

Perhaps worth noting: this is an astable sorting algorithm. The relative positions between say "beer" and "ducks" won't be preserved

Omer Tekbiyik Over a year ago

Set object is an unordered collection type so the output won't always be the same

CloudBalancing Over a year ago

True, But there was no definition on how to order the shared interest, a simple sort can do that... Nevertheless @Alexander comment on the question itself provide a solution, in case of keeping the original order it is preferable!

Alexander Over a year ago

@CloudBalancing It might be fine, or it might not, it depends on OP's goals. Sorting the result can give a consistent output, but if keeping most of the original is what he's after, that order would be hard to "bring back"

CloudBalancing Over a year ago

True that is why I considered your solution preferable

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