How to Change Values Inside Array Without a Loop Swift

How to update all items in Array in the correct way

You want to multply all items in the array with the double value of the text field.

A very suitable way in Swift is map

var receivedRates = [1.1, 1.6, 2.0, 1.3]

receivedRates = receivedRates.map{ $0 * Double(inputTextField.text!)! }

Alternatively you can enumerate the indices and update the values in place

receivedRates.indices.forEach{ receivedRates[$0] *= Double(inputTextField.text!)! }

I doubt that you really want to convert the text first to Int (losing the fractional part) and then to Double and of course you should unwrap the optionals safely.

Not able to change the value of element of array in for-loop in Swift

You might expect the loop using enumerated() to behave the same as looping over the indices and having let item = arr3[index]:

for index in arr3.indices {
    let item = arr3[index]
    print(item)
    if index+1 != arr3.count {
       arr3[index + 1] += 1
    }
}

However, this is not true. enumerated() produces an EnumeratedSequence<[Int]>. (See the source code for EnumeratedSequence and enumerated()). To create an EnumeratedSequence, the original array arr3 is passed to its initialiser:

public func enumerated() -> EnumeratedSequence<Self> {
    return EnumeratedSequence(_base: self)
}

As you may know, Array is a (copy-on-write) value type. When you modify arr3 in the loop, a modified copy is created and assigned to arr3, and the array that the EnumeratedSequence has (i.e. the array over which the loop is iterating), is unaffected. enumerated() is sort of creating a "snapshot" of the array at the time when you called it, so all the print(item) will only print the old items.

Iterate through Swift array and change values

I found a simple way and would like to share it.

The key is the definition of myArray. It would success if it's in this way:

 let myArray : [NSMutableDictionary] = [["firstDict":1, "otherKey":1], ["secondDict":2, "otherKey":1], ["lastDict":2, "otherKey":1]]

 myArray.enumerated().forEach{$0.element["index"] = $0.offset}

 print(myArray)

 [{
firstDict = 1;
index = 0;
otherKey = 1;
 }, {
index = 1;
otherKey = 1;
secondDict = 2;
}, {
index = 2;
lastDict = 2;
otherKey = 1;
}]

I have two array. How Can I change different value in Array?

Not sure if that's what you are asking again. But if I understood correctly make your CountryData conform to Equatable, iterate your countries indices and if favCountries contains the current element change the countries isSelected property to true:

---

extension CountryData: Equatable {
    public static func ==(lhs: Self, rhs: Self) -> Bool {
        lhs.name == rhs.name // match the appropriate properties
    }
}

---

countries.indices.forEach { index in
    if favCountries.contains(countries[index]) {
        countries[index].isSelected = true
    }
}

Change value in array in order

First zip the collection elements with their indices and sort by their elements in decreasing order.
Create rank and maxValue vars.

Create an array with exact same number of elements for storing the result.

Iterate the elements and indices.

If the element is less than maxValue minus one increase the rank value, update the maxValue and store the rank at the corresponding position of the original element at the resulting array:

let arr =  [5, 55, 100, 2, 99, 100, 98]

let indexedElements = zip(arr.indices, arr).sorted(by: { $0.1 > $1.1 })
var rank = 1
var maxValue = indexedElements.first?.1 ?? .max
var result = Array(repeating: 0, count: arr.count)
for index in indexedElements.indices {
    let element = indexedElements[index].1
    if element < maxValue - 1 {
        rank += 1
        maxValue = element
    }
    result[indexedElements[index].0] = rank
}
print(result)  // "[4, 3, 1, 5, 1, 1, 2]\n"

How to update a specific property value of all elements in array using Swift

You just need to iterate your array indices using forEach method and use the array index to update its element property:

struct ViewHolder {
    let name: String
    let age: Int
    var isMarried: Bool
}

var viewHolders: [ViewHolder] = [.init(name: "Steve Jobs", age: 56, isMarried: true),
                                 .init(name: "Tim Cook", age: 59, isMarried: true)]

viewHolders.indices.forEach {
    viewHolders[$0].isMarried = false
}

viewHolders  // [{name "Steve Jobs", age 56, isMarried false}, {name "Tim Cook", age 59, isMarried false}]

---

You can also extend MutableCollection and create a mutating method to map a specific property of your collection elements as follow:

extension MutableCollection {
    mutating func mapProperty<T>(_ keyPath: WritableKeyPath<Element, T>, _ value: T) {
        indices.forEach { self[$0][keyPath: keyPath] = value }
    }
}

---

Usage:

viewHolders.mapProperty(\.isMarried, false)
viewHolders  // [{name "Steve Jobs", age 56, isMarried false}, {name "Tim Cook", age 59, isMarried false}]

Find an item and change value in custom object array - Swift

Since you are using a class, use filter and first to find the value:

array.filter({$0.eventID == id}).first?.added = value

In this you:

1. filter the array down to elements that match the event ID
2. pick the first result, if any
3. then set the value

This works since classes are pass by reference. When you edit the return value from array.filter({$0.eventID == id}).first?, you edit the underlying value. You'll need to see the answers below if you are using a struct

EDIT: In Swift 3 you can save yourself a couple of characters

array.first({$0.eventID == id})?.added = value

EDIT: Swift 4.2:

array.first(where: { $0.eventID == id })?.added = value
array.filter {$0.eventID == id}.first?.added = value

---

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