struct Item {
    let name: String?
    let itemId: String?
}

let dict: [String: [Item]] = ["price": [Item(name: "10-25", itemId: "10-25")],
                              "publisher": [Item(name: "ABCD", itemId: "576"),
                                            Item(name: "DEFG", itemId: "925"),
                                            Item(name: "HIJK", itemId: "1737")]]

var keys = ["price", "publisher"]
let reduced = keys.reduce(into: [String]()) { result, current in
    guard let items = dict[current] else { return }
    let itemsStr = items.compactMap {$0.itemId }.joined(separator: ",")
    result.append("\(current):\(itemsStr)")
}
let finalStr = reduced.joined(separator: ";")
print(finalStr)