您可以对编写的代码进行一点修改，通过检查ids是否包含Post的id，而不是仅将其与ids中的第一个值进行比较，来过滤掉单个Post：

fun main() {
    // list of ids to be filtered    
    val ids = listOf("1", "5", "19")
    // list of posts to filter from
    val posts = listOf(
                    Post("1"), Post("2"),
                    Post("3"), Post("5"),
                    Post("9"), Post("10"),
                    Post("15"), Post("19"),
                    Post("20")
                )
    // filter a single post that matches the first id from ids
    val singleOutput = posts.filter { it.id == ids[0] }
    // filter all posts that have an id contained in ids
    val multiOutput = posts.filter { ids.contains(it.id) }
    // print the single post with the matching id
    println(singleOutput)
    // print the list of posts with matching ids
    println(multiOutput)
}

此操作的输出为

[Post(id=1)]
[Post(id=1), Post(id=5), Post(id=19)]

您只需要在筛选函数中使用'any'来比较所有列表元素。

val output = posts.filter { post -> ids.any { id -> id == post.id } }