Get count of Observable array before returning it

Question

In my ViewModel file I have an observable array created after applying map on it. Now before returning it I want to check if it has any content or not. If there is nothing in there I want to return it without applying map. Following is my code:

func retrieveDeals(location: CLLocation?) -> Observable<[SaleItem]> {
    let specials = nearestFlightSpecials.retrieveNearestFlightSpecials(userLocation: location)
    let happyHourDeals = specials.map {
        $0.filter { $0.isHappyHour }
    }
    return happyHourDeals
}

Before I return happyHourDeals I want to check if it contains any element or not. The above array is subscribed in view but I don't want to apply the above logic there. I want to keep it here in ViewModel.

If the array is empty nothing will be done really when calling map so I see no gain in changing your code. If you insist on checking then use isEmpty — Joakim Danielson

Daniel T. Daniel T. · Accepted Answer · 2021-02-10T12:52:46

I suspect what you want to do is filter out empty output:

func retrieveDeals(location: CLLocation?) -> Observable<[SaleItem]> {
    let specials = nearestFlightSpecials.retrieveNearestFlightSpecials(userLocation: location)
    let happyHourDeals = specials.map {
        $0.filter { $0.isHappyHour }
    }
    .filter { !$0.isEmpty } // this is the line you need.
    return happyHourDeals
}

Terminology is important here. Observables don't "contain" values. Observables don't return values, they emit events.

Your happyHourDeals will still be returned but with the filter line, it will no longer emit empty arrays. What this means is that whatever is subscribed to the value returned will not be updated if specials.map { $0.filter { $0.isHappyHour } } emits an empty array.

Get count of Observable array before returning it

1 Answers