Find object value at index and store it in different array using swift

Question

Find object value at index and store it in a different array using swift.

Can someone tell me the most optimized way for the following code snippet

    var selectedIndex = [1,3,5]
    var allData : [Person] = []
    var ids: [Int] = []
    for (index, item) in allData.enumerated() {
        for id in selectedIndex {
            if id == index {
                ids.append(item.id)
            }
        }
    }

"the most optimized way"? ids = [allData[1].id,allData[3].id,allData[5].id] — Joakim Danielson
– Joakim Danielson, Commented Oct 14, 2020 at 14:32
@JoakimDanielson Nothing wrong asking how to optimize his code. As it is he is unnecessarily iterating all elements in his collection. — Leo Dabus
– Leo Dabus, Commented Oct 14, 2020 at 14:53

Leo Dabus · Accepted Answer · 2020-10-14 14:47:08Z

3

If you are sure that all indices are valid you can simply map your selected indices:

let ids = selectedIndex.map { 
    allData[$0].id
}

If you want to make sure the selected index exists in allData:

let ids = selectedIndex.compactMap {
    allData.indices ~= $0 ? allData[$0].id : nil
}

answered Oct 14, 2020 at 14:47

Leo Dabus

237k61 gold badges512 silver badges624 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

user652038 · Accepted Answer · 2020-10-14 15:17:06Z

0

Because your indices are sorted, you can take just the portion of allData that you need, using prefix.

let ids =
  allData
  .prefix(selectedIndices.last.map { $0 + 1 } ?? 0)
  .enumerated()
  .compactMap {
    Optional($0)
      .filter { selectedIndices.contains($0.offset) }?
      .element.id
  }

public extension Optional {
  /// Transform `.some` into `.none`, if a condition fails.
  /// - Parameters:
  ///   - isSome: The condition that will result in `nil`, when evaluated to `false`.
  func filter(_ isSome: (Wrapped) throws -> Bool) rethrows -> Self {
    try flatMap { try isSome($0) ? $0 : nil }
  }
}

answered Oct 14, 2020 at 15:17

user652038

Collectives™ on Stack Overflow

Find object value at index and store it in different array using swift

2 Answers 2

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related