Swift - Sorting array of objects by another array's property

Question

I want to sort an Array of objects, by the properties it shares with another Array of objects

    struct GeneralComposition : Decodable {
        let id, formId, relationId, fixedContentTypeId, separatorId: Int
        let orderBy: Int

    }
    struct FixedContentType: Decodable {
        let name, htmlType: String
        let isEditable: Int
        let typeId : String


    }



   var fixedContentType = [FixedContentType]()
   var generalComposition = [GeneralComposition]()

In GeneralComposition I get the order the items must have, with orderBy, and then take every item's fixedContentTypeID, compare with the typeId in FixedContentType to get the order in which this content must be showed in screen.

Any idea about how can it be done?

Thanks!

@matt - That looks like a duplicate, but isn’t quite the same. That indexOf pattern is not applicable here. — Rob
– Rob, Commented Mar 16, 2019 at 14:00
Cosorting is cosorting it seems to me. It’s not like it’s never been discussed before. — matt
– matt, Commented Mar 16, 2019 at 14:02
Maybe, we can find a consorting example where it’s not relying on the index(of:) the identifier in the second array, but rather a property of the objects in that second array, like this one. I looked and one didn’t jump out at me, but I bet there’s one out there... — Rob
– Rob, Commented Mar 16, 2019 at 14:30

Rob · Accepted Answer · 2019-03-16 10:21:12Z

4

You can build a dictionary for the fixedContentTypeID’s of generalComposition:

let order = generalComposition.reduce(into: [Int: Int]()) { result, value in
    result[value.fixedContentTypeId] = value.orderBy
}

You now have an efficient way to lookup the orderBy value for a given typeId within your array of FixedContentType objects. You can use that for sorting:

fixedContentType.sort {
    (order[$0.typeId] ?? 0) < (order[$1.typeId] ?? 0)
}

By the way, your typeId is a String, and fixedContentTypeId is an Int. I’m assumed that was a typo introduced when preparing the question, and that they’re really both Int. If they’re really different types (which would be weird), the solution would be similar, though you’d have to do some conversions. But I didn’t want to go there unless you confirmed that this is really what you model was.

But, given that your typeId really is a String, you could make your dictionary a [String: Int]:

let order = generalComposition.reduce(into: [String: Int]()) { result, value in
     result[String(value.fixedContentTypeId)] = value.orderBy
}

edited Mar 16, 2019 at 10:21

answered Mar 16, 2019 at 0:04

Rob

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7 Comments

Mohmmad S Over a year ago

What about a protocol ?

Mohmmad S Over a year ago

make protocol that have the shared properties and an array of this protocol and sort that ?

Rob Over a year ago

I’d suggest you post you own answer showing how you’d propose using a protocol. I personally don’t see how that would help. The main thrust of my answer is using a dictionary to achieve O(1) performance for the retrieval of the orderBy values.

Mohmmad S Over a year ago

if i wanted to answer i would've i want to know the difference and gain exp from the high tier ^_^ thanks anyway

Mohmmad S Over a year ago

one day i will care about the O(1), just like you do sir.

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