drop(where: {}) remove(where: {}) function in Swift?

Question

Is there a function in the Swift Standard library that acts on a collection, takes a predicate and returns the value removed from that collection?

Currently, I have to implement it in 2 steps:

guard let idx = allAnnotations.index(where: {$0 is MKUserLocation}) else {return}
let userLocation = allAnnotations.remove(at: idx) as! MKUserLocation

But I guess, a similar function exists.

The goal

I have the following array:

[Type1, Type1, Type1, Type1, Type1, Type1, Type2]

Type2 may or may not be present in the array. There are no other types except these two.

I need to split it onto two elements:

[Type1, Type1, Type1, Type1, Type1, Type1]

and

Type2?

That's the function I'm looking for.

sounds like you are looking for [`filter()`](https://developer.apple.com/documentation/swift/sequence/2905694-filter) — vikingosegundo, May 04 '18 at 09:12
What is expected if more than one element, matches with the predicate? Currently you are removing the first one. — Puneet Sharma, May 04 '18 at 09:18
@vikingosegundo true, filter is close. I've updated the question to clarify it a bit more. — Richard Topchii, May 04 '18 at 09:19
What if there are multiple elements of Type2, and also some elements of Type3? — Martin R, May 04 '18 at 09:20
@PuneetSharma Yes, it's fine. There may be only one element of `Type2`. In particular, I'm splitting `[MKAnnotation]` into an array of my custom annotations and `MKUserLocation` annotation. — Richard Topchii, May 04 '18 at 09:20
@RichardTopchiy https://stackoverflow.com/a/47544741/2303865 — Leo Dabus, May 04 '18 at 10:40

score 4 · Accepted Answer · edited Sep 09 '21 at 18:07

4

Swift 5 has removeAll(where)

@inlinable public mutating func removeAll(where shouldBeRemoved: (Element) throws -> Bool) rethrows

You can use it like this -

var array = [1,2,3]
array.removeAll(where: { $0 == 2})
print(array) // [1,3]

Apple Docs

edited Sep 09 '21 at 18:07

Pranav Kasetti

8,770
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answered Jun 19 '19 at 12:11

shannoga

19,649
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169

Thank you for your answer, I'll mark it as accepted since Swift 5 is the mainstream now. My question was written prior to Swift 5. – Richard Topchii Jun 19 '19 at 12:15

score 2 · Answer 2 · answered May 04 '18 at 09:27

Here is an extension that returns an array of dropped elements:

extension Array {
    mutating func dropWhere(_ isIncluded: (Element) throws -> Bool) -> [Element] {
        do {
            let reverseArray = try filter { try isIncluded($0) }
            self = try filter { try !isIncluded($0) }

            return reverseArray
        } catch {
            return []
        }
    }
}

Just call it like you would call filter.

var array = [1, 2, 3]
let array2 = array.dropWhere { $0 > 2 }
print(array) //[1, 2]
print(array2) //[3]

score 2 · Answer 3 · answered May 09 '18 at 12:55

Code I've finished with:

extension Array {
  mutating func popFirstElementWith(_ predicate:(Element)->(Bool)) -> Element? {
    for (idx, element) in enumerated() {
      if predicate(element) {
        remove(at: idx)
        return element
      }
    }
    return nil
  }
}

score 1 · Answer 4 · answered May 04 '18 at 09:27

1

you can use Split on condition will slice your array

    var typeList =  [Type1, Type1, Type1, Type1, Type1, Type1, Type2]

    var slicedArray:[ArraySlice] = typeList.split { (value) -> Bool in
                return value == YourCondition
            }
print(slicedArray)

answered May 04 '18 at 09:27

Abdelahad Darwish

5,969
1
17
35

1

`Split` wouldn't work if the element of `Type2` is not at the beginning/end of the array. – Richard Topchii May 09 '18 at 12:24

score 1 · Answer 5 · answered May 04 '18 at 09:33

1

This extension takes a predicate and returns the element if it matches the predicate. Also, removes the element from the array.

extension Array {
    mutating func popFirstElementWith(_ predicate:(Element)->(Bool)) -> Element? {
        var firstElement:Element?
        self = self.compactMap({ (element:Element) -> Element? in
            guard predicate(element) == true else {
                return element
            }
            if firstElement == nil {
                firstElement = element
            }
            return nil
        })
        return firstElement
    }
}

TEST:

var array:[Any] = ["a", "b", 1, "c"]
let element = array.popFirstElementWith { (element) -> (Bool) in
    return element is Int
}
print(element!)
print(array)

Output:

1
["a", "b", "c"]

answered May 04 '18 at 09:33

Puneet Sharma

9,369
1
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Thank you. While the Swift standard library doesn't have such a function, I've accepted your answer. That's exactly what's needed. – Richard Topchii May 09 '18 at 12:28
I've modified your code a bit, please take a look at my answer below. – Richard Topchii May 09 '18 at 12:55
@RichardTopchiy: In your code you are deleting the first element you found that matches the predicate and return. I guess, it is fine if that is what you desired. – Puneet Sharma May 09 '18 at 13:02
True, it works exactly the same way as your example. It's fine for my task, as I have only one object to remove. – Richard Topchii May 09 '18 at 17:55

drop(where: {}) remove(where: {}) function in Swift?

5 Answers5