Filter array of custom objects with an attribute and Map in Swift

Question

My model class is as below :

struct Job: Decodable, Equatable, Hashable {
   var id: Int?
   var status: String?
   var priority: String?
}

I have 2 array of objects(job) as :

 var jobModel = [Job]()
 var filteredJobModel = [Job]()

Case : jobModel has 5 elements. filteredJobModel has 2 elements( subset of jobModel ). In filteredJobModel, the value for status for both objects has been changed by search operation. I would like to update the jobModel back with filteredJobModel, where the object matches the id attribute.

Is there any way by which I can achieve this case? I would have been able to use filter & map for [String], but, I would like to know how to implement higher order functions for array of custom objects.

Duncan C · Accepted Answer · 2019-11-28 02:24:58Z

1

for (index, job) in idsJobModel.enumerated() {
    if let match = arrFiltetered.first( where: {job.id == $0.id} ) {
     idsJobModel[index] = match
   }
}

Or if you prefer using map:

idsJobModel = idsJobModel.map {
    let myID = $0.id
    if let match = arrFiltetered.first( where: {myID == $0.id} ) {
        return match
    } else {
        return $0
    }
}

Either version of the code above will have O(n²) performance, so it will get dramatically slower as your arrays get larger than ≈30 elements. It would need to be tweaked to perform well on larger arrays.

edited Nov 28, 2019 at 2:24

answered Nov 28, 2019 at 2:08

Duncan C

132k22 gold badges185 silver badges294 bronze badges

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

2 Comments

Duncan C Over a year ago

Assuming the id value in idsJobModel is always unique (and never nil), you could improve the performance of the above by mapping the arrFiltetered array into a dictionary using the id as a key. you'd then loop through idsJobModel , do a dictionary lookup of each ID, and replace the entry in idsJobModel if found as above (dictionary lookups are almost O(1), so that would improve your performance to roughly O(n), a dramatic improvement.

Duncan C Over a year ago

Even if your id values are not unique you could implement a custom hash function that excludes your (changeable) status property and use the hash as your dictionary key in the above speed optimization.

Collectives™ on Stack Overflow

Filter array of custom objects with an attribute and Map in Swift

1 Answer 1

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related