How to use Combine collect method after a map - swift

Question

I would like to use the collect method of Combine to split an array of objects into Array of multiples Arrays which would correspond to Rows in a Collection View (eg: [Item, Item, Item, Item, Item] would become [[Item, Item, Item], [Item, Item]] and so on)
My data is coming from two publisher that I'm chaining to merge my data into a single type consumed by my view.
Here is my code :
APIClient().send(APIEndpoints.searchMovies(for: text)).flatMap { response -> AnyPublisher<APIResponseList<TVShow>, Error> in
movies = response.results.map { SearchItemViewModel(movie: $0)}
return APIClient().send(APIEndpoints.searchTVShows(for: text))
}
.map { response -> [SearchItemViewModel] in
tvShows = response.results.map { SearchItemViewModel(tvShow: $0)}
let concatItems = tvShows + movies
return concatItems.sorted { $0.popularity > $1.popularity }
}
.collect(3)
.sink(receiveCompletion: { (completion) in
switch completion {
case .failure:
self.state = .error
self.items = []
case .finished:
break
}
}, receiveValue: { (response) in
self.state = .data
self.items = response
})
.store(in: &disposables)
My problem currently is that inside my sink receiveValue closure, the response parameter doesn't equal the expected result, it just group all my items into an array like this : [Item, Item, Item, Item, Item] -> [[Item, Item, Item, Item, Item]]
It seems that the collect method is not working as expected, any idea about how I could fix this ?

Answer 1

it just group all my items into an array like this : [Item, Item, Item, Item, Item]
Pass that through a flatMap and generate its Sequence publisher. Now the Item objects will arrive one at a time and collect(3) will work as you expect.
Example:
var storage = Set<AnyCancellable>()
let head = Just([1,2,3,4,5]) // this is the same as your `.map`
head
.flatMap { $0.publisher }
.collect(3)
.sink{print($0)} // prove that it works: [1, 2, 3], then [4, 5]
.store(in: &storage)

Answer 2

Create this extension:
extension Array {
func split(numItems:Int) -> [[Element]] {
var i = 0
var ret = [[Element]]()
var current = [Element]()
while i < self.count {
current.append(self[i])
i += 1
if i % numItems == 0 {
ret.append(current)
current = []
}
}
if current.count > 0 {
ret.append(current)
}
return ret
}
}
Now, you should be able to do this:
APIClient().send(APIEndpoints.searchMovies(for: text)).flatMap { response -> AnyPublisher<APIResponseList<TVShow>, Error> in
movies = response.results.map { SearchItemViewModel(movie: $0)}
return APIClient().send(APIEndpoints.searchTVShows(for: text))
}
.map { response -> [SearchItemViewModel] in
tvShows = response.results.map { SearchItemViewModel(tvShow: $0)}
let concatItems = tvShows + movies
var sorted = concatItems.sorted { $0.popularity > $1.popularity }
return sorted.split(numItems:3)
}
.sink(receiveCompletion: { (completion) in
switch completion {
case .failure:
self.state = .error
self.items = []
case .finished:
break
}
}, receiveValue: { (response) in
self.state = .data
self.items = response
})
.store(in: &disposables)