从映射中剪切具有空值的对

Question

我想过滤掉所有具有空值的对

val mapOfNotEmptyPairs: Map<String, String> = mapOf("key" to Some("value"), "secondKey" to None)

预期：

print(mapOfNotEmptyPairs)
// {key=value}

Answer 1

香草科特林

val rawMap = mapOf<String, String?>(
"key" to "value", "secondKey" to null)

// Note that this doesn't adjust the type. If needed, use
// a cast (as Map<String,String>) or mapValues{ it.value!! }
val filteredMap = rawMap.filterValues { it != null }
System.out.println(filteredMap)

p.s使用箭头选项时

val rawMap = mapOf<String, Option<String>>(
mapOf("key" to Some("value"), "secondKey" to None)
val transformedMap = rawMap
.filterValues { it.isDefined() }
.mapValues { it.value.orNull()!! } 

p.p.s使用Arrow Option及其filterMap扩展函数时；

val rawMap = mapOf<String, Option<String>>(
mapOf("key" to Some("value"), "secondKey" to None)
val transformedMap = rawMap
.filterMap { it.value.orNull() } 

Answer 2

val mapOfNotEmptyPairs =
mapOf("key" to Some("value"), "secondKey" to None)
.filterValues { it is Some<String> } // or { it !is None } or { it.isDefined() }
.mapValues { (_, v) -> (v as Some<String>).t }