Using pattern matching to filter array

Question

this is my code:

enum SymptomPeriod {
    case Day
    case Night
}

enum SymptomType {

    case Breathing(SymptomPeriod) 
    case Breathlessness(SymptomPeriod) 
    case Opression(SymptomPeriod) 
    case Cough(SymptomPeriod) 

    case ActivityLimited() 
    case SecureTreatment() 
}

struct Symptom {
    let type: SymptomType
    let date: NSDate
}

And i have an array of symptoms.

let symptomList: [Symptom] = ...

My need is to filter the list of symptoms with the SymptomPerion criteria, i trying to do like this:

 let daySymtoms = symptomList.filter { (symptom) -> Bool in
    return symptom.type = ???
 }

My problem is in the filter function.

(My goal is to use a filter function and not a loop)

Luca Angeletti · Accepted Answer · 2016-06-22 00:41:53Z

2

A few suggestions

Use your struct as namespace

Instead of repeating the word Symptom (e.g. SymptomPeriod, SymptomType) you should put your enums into you Symptom struct

Rename SymptomType as Kind

Once you moved SymptomType into Symptom you can drop the Symptom part of the name. However using Type as name will create a conflict so you should rename it Kind.

Add the period computed property to Kind

This will make the filtering much easier

Here's the code

struct Symptom {
    enum Period {
        case Day
        case Night
    }

    enum Kind {
        case Breathing(Period)
        case Breathlessness(Period)
        case Opression(Period)
        case Cough(Period)

        case ActivityLimited()
        case SecureTreatment()

        var period: Period? {
            switch self {
            case Breathing(let period): return period
            case Breathlessness(let period): return period
            case Opression(let period): return period
            case Cough(let period): return period
            default: return nil
            }
        }
    }

    let kind: Kind
    let date: NSDate
}

The solution

Now the filtering has become very easy

let symptoms: [Symptom] = ...
let filtered = symptoms.filter { $0.kind.period == .Day }

edited Jun 22, 2016 at 0:41

answered Jun 20, 2016 at 23:49

Luca Angeletti

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1 Comment

Nicolas Miari Over a year ago

Very nice. But there is a lot of case XXXX(let period): return period. I wish Swift had a way of avoiding such repetition.

samir · Accepted Answer · 2016-06-20 23:12:21Z

0

This is how i am doing it:

let daySymtoms = symtoms.filter { (symptom) -> Bool in
            switch symptom.type {
            case .Breathing(.Day), .Breathlessness(.Day), .Opression(.Day), .Cough(.Day):
                  return true

            default:
                  return false
            }
         }

Let me know if you have more simple way to do it.

answered Jun 20, 2016 at 23:12

samir

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Using pattern matching to filter array

2 Answers 2

Use your struct as namespace

Rename SymptomType as Kind

Add the period computed property to Kind

Here's the code

The solution

1 Comment

Comments

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Collectives™ on Stack Overflow

2 Answers 2

Use your struct as namespace

Rename SymptomType as Kind

Add the period computed property to Kind

Here's the code

The solution

1 Comment

Comments

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