从地图中剪切具有空值的对

问题描述

我想过滤掉所有空值对

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

预期：

print(mapOfNotEmptyPairs)
// {key=value}

解决方法

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 当使用 Arrow Option 和它们的 filterMap 扩展函数时；

val rawMap = mapOf<String,"secondKey" to None)

val transformedMap = rawMap
   .filterMap { it.value.orNull() } 

,

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 }