Filter data in less time

Question

I have 2000 contacts and i want to find duplicates and the filter is taking like 1min to find duplicates.

let duplicateArray = contacts.filter { value in 
    contacts.filter({ 
        $0.phoneNumbers.first?.value.value(forKey: "stringValue") as? 
        String ?? "" == value.phoneNumbers.first?.value.value(forKey: 
        "stringValue") as? String ?? "" 
    }).count > 1  
}

https://stackoverflow.com/questions/29727618/find-duplicate-elements-in-array-using-swift ? — Larme, Sep 10 '19 at 10:34
You can use `Set`. You have require to confirm `Equatable ` protocol for your custom class. — Pratik Sodha, Sep 10 '19 at 10:52
i want to fetch both duplicate number eg: let array = [1,2,3,3] so output must be [3,3] — Siddhant Kuldeep, Sep 10 '19 at 11:02
I'd suggest using Core Data and keeping your contacts in a database. It's super fast for searching & sorting. — David Steppenbeck, Sep 10 '19 at 11:19
@DavidSteppenbeckPhD i had used CoreData but it takes 45sec just to add 2000 data — Siddhant Kuldeep, Sep 10 '19 at 11:28
@SiddhantKuldeep I'm surprised it took that long. Were you updating/adding in small batches (groups of ~50 objects) rather than all 2000 at once? — David Steppenbeck, Sep 10 '19 at 11:31
@DavidSteppenbeckPhD in viewillappear i was adding all 2000 contacts in CoreData — Siddhant Kuldeep, Sep 10 '19 at 12:17

score 2 · Answer 1 · answered Sep 10 '19 at 11:10

2

Let's consider this array

let array = [1,2,3,4,3,2]

Using a dictionary, let's count how many times each element appears in the array:

var dict : [Int: Int] = [:]

for element in array {
    dict[element, default: 0] += 1
}

Now let's construct a new array that contains the elements that appear more than once in the original array:

var output = dict.flatMap { (key, value) in
    return Array(repeating: key, count: value == 1 ? 0 : value)
}

print(output)  //[3, 3, 2, 2]

answered Sep 10 '19 at 11:10

ielyamani

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I was doing this same answer but just before you submitted it :p. – Shivam Gaur Sep 10 '19 at 11:12
@ShivamGaur maybe next time ;) – ielyamani Sep 10 '19 at 11:14

score 1 · Answer 2 · edited Sep 11 '19 at 07:08

1

A good way to remove duplicates is using the Set(), since a Set can only contain one of each element

let duplicates = [1, 2, 3, 3]
let unique = Set(duplicates) // will only contain 1, 2 and 3

edited Sep 11 '19 at 07:08

PGDev

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answered Sep 10 '19 at 10:36

magnuskahr

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but i want output as: [3,3] – Siddhant Kuldeep Sep 10 '19 at 10:54

score 0 · Answer 3 · answered Sep 10 '19 at 10:39

You can use something like this

extension Array where Element: Hashable {
   func removingDuplicates() -> [Element] {
       var addedDict = [Element: Bool]()

       return filter {
           addedDict.updateValue(true, forKey: $0) == nil
       }
   }

   mutating func removeDuplicates() {
       self = self.removingDuplicates()
   }
}

score 0 · Accepted Answer · answered Sep 10 '19 at 10:57

0

Since you only want the duplicated, use a combination of Dictionary's init(grouping:by:), filter(_:) and flatMap(_:).

Example:

let arr = [1, 1, 3, 1, 2, 2, 4]
let result = Dictionary(grouping: arr, by: { $0 }).filter({ $0.1.count > 1 }).flatMap({ $0.value })

print(result) //[2, 2, 1, 1, 1]

answered Sep 10 '19 at 10:57

PGDev

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this filter is taking 2mins to filter 2000 data – Siddhant Kuldeep Sep 10 '19 at 11:10
1

Are you sure @SiddhantKuldeep? I can run it in 33ms – magnuskahr Sep 10 '19 at 12:57
@SiddhantKuldeep It isn't. Kindly add the method you're using to calculate the execution time. It is taking somewhere around 30-40ms. – PGDev Sep 10 '19 at 13:24

Filter data in less time

4 Answers4