The following code (written in Kotlin) extracts the elements from a list of lists. It works, but looks rather ugly and difficult to read.
Is there a nicer way to write the same with the java stream api? (Examples can be given in Kotlin or Java)
val listOfLists: List<Any> = ...
val outList: MutableList<Any> = mutableListOf()
listOfLists.forEach {
list ->
if (list is ArrayList<*>) list.forEach {
l ->
outList.add(l)
}
}
return outList;
In Kotlin it's super easy without any excessive boilerplate:
val listOfLists: List<List<String>> = listOf()
val flattened: List<String> = listOfLists.flatten()
flatten() is the same as doing flatMap { it }
In Java, you need to utilize Stream API:
List<String> flattened = listOfLists.stream()
.flatMap(List::stream)
.collect(Collectors.toList());
You can also use Stream API in Kotlin:
val flattened: List<String> = listOfLists.stream()
.flatMap { it.stream() }
.collect(Collectors.toList())
You could flatMap each list:
List<List<Object>> listOfLists = ...;
List<Object> flatList =
listOfLists.stream().flatMap(List::stream).collect(Collectors.toList());
Use flatMap
List<Integer> extractedList = listOfLists.stream().flatMap(Collection::stream).collect(Collectors.toList());
flatMap() creates a stream out of each list in listOfLists. collect() collects the stream elements into a list.
