Say I have multiple (MANY) Lists, each containing multiple Record objects that contain one long constructor parameter "time" (and a string parameter for debugging purposes).
Here is an example:
val list1 = listOf(Record(0, "A1"), Record(1, "A2"), Record(2, "A3"))
val list2 = listOf(Record(0, "B1"), Record(2, "B2"))
val list3 = listOf(Record(1, "C1"), Record(2, "C2"))
I want to combine the lists into one list, so that at any given time present in the original lists, the latest value from each list is present in the list.
Here is an example:
val output = listOf(Record(0, "A1+B1"), Record(1, "A2+B1+C1"), Record(2, "A3+B2+C2"))
Assume that Records can be added to create new Records containing the data of both.
(Technically, Records are a typealias for a key-value map containing data, but I thought that was out of scope for this question.)
you can use 'associateByTo' inline method. Assuming that：
data class Record(val time: Int, var text: String)
then：
val list1 = listOf(Record(0, "A1"), Record(1, "A2"), Record(2, "A3"))
val list2 = listOf(Record(0, "B1"), Record(2, "B2"))
val list3 = listOf(Record(1, "C1"), Record(2, "C2"))
val map = hashMapOf<Int, Record>()
val output = listOf(list1, list2, list3).flatten().associateByTo(map,
{ it.time },
{
//if the record id exist in map, append time
map[it.time]?.apply { text += "+${it.text}" } ?: it
})
println(output.values)
output.values are what you want.
Assuming that
data class Record(val time:Long , val param2:String)
Then you can do like this
val list1 = listOf(Record(0, "A1"), Record(1, "A2"), Record(2, "A3"))
val list2 = listOf(Record(0, "B1"), Record(2, "B2"))
val list3 = listOf(Record(1, "C1"), Record(2, "C2"))
val output = listOf(list1,list2,list3)
.flatten()
.groupBy { it.time }
.map { (key,value) ->
// you could define your own separator if needed
val newParam2 = value.joinToString(separator = "+") { it.param2 }
Record(key,newParam2)
}
println(output)
//[Record(0, "A1+B1"), Record(1, "A2+B1+C1"), Record(2, "A3+B2+C2")]