how do you take an Observable<Spot> which ha...

# android

[lawlorslaw]

how do you take an Observable<Spot> which has N emissions and turn it into a Single<List<Spot>> which has all N emissions?

[Tobi]

You could do it using a reducer function to first change it from Observable<Spot> to Observable<List<Spot>> and then transform it to a Single<List<Spot>>

[Tobi]

http://reactivex.io/documentation/operators/reduce.html

[edwardwongtl]

A simple .toList() on a Observable<T> will be enough.

[lawlorslaw]

.toList() turns it into a MutableList and not a List in Kotlin

[edwardwongtl]

It is simple to convert a Mutable list to a List…

[lawlorslaw]

How do you do that?

[edwardwongtl]

Also .toList()

[Tobi]

🤦‍♂️ yes, go for toList()

[Paul Woitaschek]

That makes no sense. MutableList : List

[edwardwongtl]

That's why the toList function is just returning the same inatance typecasted to List. It does not create a new list and do all the stupid copying.

[Paul Woitaschek]

But you don't need kotlin's .toList

[Paul Woitaschek]

fun test(): Single<List<Int>> {
return Observable.just(1, 2, 3).toList()
}

[Paul Woitaschek]

If I understand correctly you suggested to call toList inside a map

[edwardwongtl]

You're right, the toList call is not really needed.

[Paul Woitaschek]

I mean the issue here might be that you might remove items from the list

[Paul Woitaschek]

Observable.just(1, 2).toList().doOnSuccess { it.remove(0) }

[Paul Woitaschek]

When you call kotlin.toList it internally calls toMutableList if it has more than 1 entry.