let allKeys = Set(dict1.keys).union(dict2.keys)

    let output = allKeys.reduce(into: [String: [Int: [FinalModel]]]()) { partialResult, currentDateKey in
        let firstModels: [FirstModel]? = dict1[currentDateKey]
        let secondModels: [SecondModel]? = dict2[currentDateKey]
        let allIds: Set<Int> = Set(firstModels?.compactMap { $0.id } ?? []).union( secondModels?.compactMap { $0.id } ?? [])

        let models: [Int: [FinalModel]] = allIds.reduce(into: [Int: [FinalModel]]()) { partialModelResult, currentIdKey  in
            let first: [FirstModel] = firstModels?.filter { $0.id == currentIdKey } ?? []
            let second: [SecondModel]? = secondModels?.filter { $0.id == currentIdKey }
            //I supposed there can only be one SecondModel for each id
            let finalModel = FinalModel(first: first.isEmpty ? nil : first, second: second?.first)
            var currentlySaved = partialModelResult[currentIdKey, default: []]
            currentlySaved.append(finalModel)
            partialModelResult[currentIdKey] = currentlySaved
        }
        partialResult[currentDateKey] = models
    }