我試圖操縱數(shù)據(jù)的結(jié)構(gòu)，以便我可以將它傳遞給這個函數(shù)fun handleRequests(messages: Map<MessageDestination, List<MessageSender>>): Either<Errors.RequestError, Unit>。但我不斷收到此錯誤： syntaxerrorError:(27, 63) Kotlin: Type inference failed. Expected type mismatch: inferred type is Map<MessageDestination, List<Pair<MessageSender, String>>> but Map<MessageDestination, List<MessageSender>> was expected.我需要將我的數(shù)據(jù)轉(zhuǎn)換為，Map<MessageDestination, List<MessageSender>>但我不知道該怎么做。這是代碼：package testp.package1.handlersimport arrow.core.Eitherimport arrow.core.flatMapimport com.amazonaws.services.lambda.runtime.Contextimport com.amazonaws.services.lambda.runtime.RequestHandlerinterface InterfaceService { fun handleRequests(messages: Map<MessageDestination, List<MessageSender>>): Either<Errors.RequestError, Unit>}abstract class AbstractMessageHandler( override val service: InterfaceService = ServiceImpl()) : MessageHandler<MyMessage>() { abstract val emailType: ServiceImpl.Companion.EmailType override val emailParser: IMessageParser<MyMessage> = M2MessageParser() override fun handle(event: List<String>): Either<Errors.RequestError, Pair<List<Errors.RequestError>, Int>> = emailParser.parseEmails(event) .map { (error, messages) -> error to messages.map { myMessage -> MessageSender(message = myMessage.environment) to myMessage.emailAdrress } } .flatMap { (errors: List<Errors.RequestError>, emailMesssages: List<Pair<MessageSender, String>>) -> service.handleRequests(emailMesssages.groupBy { MessageDestination(it.second) }).map { Pair(errors, emailMesssages.size) } }}data class MessageDestination(val emailAddress: String)data class MyMessage(val environment: String, val emailAdrress: String, val phoneId: String)data class MessageSender(val message: String)
1 回答
holdtom
TA貢獻(xiàn)1805條經(jīng)驗(yàn) 獲得超10個贊
您想轉(zhuǎn)換按列表分組的值，因此：
emailMesssages.groupBy(
{ MessageDestination(it.second) },
{ it.first }
)
長版：
好的，所以你開始： emailMesssages: List<Pair<MessageSender, String>> 并且你想把它轉(zhuǎn)換成類型Map<MessageDestination, List<MessageSender>>
您正試圖通過emailMesssages.groupBy { MessageDestination(it.second) }. groupBy它按您指定的鍵對列表中的項(xiàng)目進(jìn)行了哪些分組。重要的是它將Pair一個鍵的所有項(xiàng)目（在本例中為所有s）組合到列表中。
所以如果你有（來自官方文檔的樣本）：
val words = listOf("a", "abc", "ab", "def", "bc")
val byLength = words.groupBy { it.length }
然后 byLength 是：
1 -> listOf("a")
2 -> listOf("ab", "bc")
3 -> listOf("abc", "def")
這解釋了為什么你有 typeMap<MessageDestination, List<Pair<MessageSender, String>>>而不是Map<MessageDestination, List<MessageSender>>.
您想要做的不是對列表中的項(xiàng)目進(jìn)行分組，而是希望對列表中的項(xiàng)目中的轉(zhuǎn)換值進(jìn)行分組。
基本上你想要的是'groupBy'的另一個變體，帶有keySelector AND valueTransform：
inline fun <T, K, V> Array<out T>.groupBy(
keySelector: (T) -> K,
valueTransform: (T) -> V
): Map<K, List<V>> (source)`
在你的情況下，這看起來像這樣：
emailMesssages.groupBy(
{ MessageDestination(it.second) },
{ it.first }
)
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