How to compare two array of objects? - ios

Question

I have a class A:
class A {
var identifier: String?
var quantity: Int = 0
}
Two arrays of A instances:
var array1: [A] = [a1, a2, a3, a4]
var array2: [A] = [a5, a6, a7, a8]
I don't know which is the best way to check:
array1==array2 if a1.identifier == a5.identifier, a2.identifier == a6.identifier, a3.identifier==a7.identifier, a4.identifier==a8.identifier in Swift.
Please help me...

Answer 1

You can try like this:
let result = zip(array1, array2).enumerated().filter() {
$1.0 == $1.1
}.map{$0.0}

Answer 2

Swift 4
The following method makes it much more easy.
Method 1 - Using Equatable Protocol
Step1 - Make your class 'A' equatable as follows
extension A: Equatable {
static func ==(lhs: A, rhs: A) -> Bool {
// Using "identifier" property for comparison
return lhs.identifier == rhs.identifier
}
}
Step2 - Sort your arrays in ascending or descending order
let lhsArray = array1.sorted(by: { $0.identifier < $1.identifier })
let rhsArray = array2.sorted(by: { $0.identifier < $1.identifier })
Step3 - Use == or elementsEqual comparison
let isEqual = lhsArray == rhsArray
OR
let isEqual = lhsArray.elementsEqual(rhsArray, by: { $0 == $1} )
Method 2 (Without Equatable Protocol)
Step 1 - Sort Array as described in Method1, step 2
Step 2 - Use elementsEqual
lhsArray.elementsEqual(rhsArray, by: { $0.identifier == $1.identifier })
Read more about Array Comparison here

Answer 3

Assume your data like that:
struct Person
{
let name: String
let id: Int
}
var people1 = [
Person(name: "Quang Hà", id: 42),
Person(name: "Lý Hải", id: 23),
Person(name: "Maria", id: 99)
]
var people2 = [
Person(name: "Maria yyy", id: 99),
Person(name: "Billy", id: 42),
Person(name: "David", id: 23)
]
This is the method to compare two arrays of people with id:
func areArrayPeopleEqual(people1:[Person], people2: [Person]) -> Bool {
var array1 = people1
var array2 = people2
// Don't equal size => false
if array1.count != array2.count {
return false
}
// sort two arrays
array1.sortInPlace() { $0.id > $1.id }
array2.sortInPlace() {$0.id > $1.id }
// get count of the matched items
let result = zip(array1, array2).enumerate().filter() {
$1.0.id == $1.1.id
}.count
if result == array1.count {
return true
}
return false
}

Answer 4

This method could be used if you have some parameter to compare:
let difference = currentObjects
.filter({ currentObject in
!(newObjects
.contains(where: { $0.identifier == currentObject.identifier }))
})

Answer 5

I found this really easy solution at https://www.hackingwithswift.com/example-code/language/how-to-find-the-difference-between-two-arrays
extension Array where Element: Hashable {
func difference(from other: [Element]) -> [Element] {
let thisSet = Set(self)
let otherSet = Set(other)
return Array(thisSet.symmetricDifference(otherSet))
}
}
let names1 = ["a1", "A4", "a3", "a4"]//["John", "Paul", "Ringo"]
let names2 = ["a1", "a5", "a4","a1.1"]//["Ringo", "George"]
let difference = names1.difference(from: names2)

Answer 6

First we extend Equatable class, to have a DRY code, than if the 2 arrays are always of the same size, or if at least the first one is <= than the second you can go with this solution.
Pay attention that you are working with optionals, you may have to unwrap them before.
class A {
var identifier: String?
var quantity: Int = 0
init(identifier: String, quantity: Int) {
self.identifier = identifier
self.quantity = quantity
}
}
let a1: A = A(identifier: "1", quantity: 1)
let a2: A = A(identifier: "2", quantity: 2)
let a3: A = A(identifier: "3", quantity: 3)
let a4: A = A(identifier: "4", quantity: 4)
let a5: A = A(identifier: "1", quantity: 1)
let a6: A = A(identifier: "2", quantity: 2)
let a7: A = A(identifier: "3", quantity: 3)
let a8: A = A(identifier: "4", quantity: 4)
var array1: [A] = [a1, a2, a3, a4]
var array2: [A] = [a5, a6, a7, a8]
func areEquals(array1: [A], array2: [A]) -> Bool {
if array1.count < array2.count {
return false
}
for i in 0...array2.count - 1 {
if array1[i] != array2[i] {
return false
}
}
return true
}
extension A: Equatable {
static func ==(lhs: A, rhs: A) -> Bool {
//you can choose how and when they should be equals
return lhs.identifier == rhs.identifier
}
}

Answer 7

try this code, let me know if it works
func toDictionary<E, K, V>(
array: [E],
transformer: (element: E) -> (key: K, value: V)?)
-> Dictionary<K, V>
{
return array.reduce([:]) {
(var dict, e) in
if let (key, value) = transformer(element: e)
{
dict[key] = value
}
return dict
}
}
then you can execute a check like below
let areEqual = array1.count == array2.count;
if areEqual {
let dict1 = toDictionary(array1) { ($0.identifier, $0.quantity) }
let dict2 = toDictionary(array2) { ($0.identifier, $0.quantity) }
areEqual = NSDictionary(dictionary: dict1).isEqualToDictionary(dict2)
}
print(areEqual)
disclaimer: function toDictionary has been took form here