How to merge nested Maps in Kotlin - kotlin

Question

I'm trying to merge values from two maps in Kotlin, but I can't seem to find a solution online to do so. For example, I have these two Map Objects that have nested maps as shown below.
first: {settings={exit={exitMessage=message0}}, 2=2}
second: {settings={exit={differentMessage=message1, secondMessage=message2}}, 2=zebra}
As you can see, there are some keys that are the same(like settings and exit), but sometimes the keys are different. I'm wondering how I can merge the two Map objects so the end result is like
{settings={exit={exitMessage=message0, differentMessage=message1, secondMessage=message2}}, 2=zebra}
We can't simply "add" the two maps together, because Kotlin will override the Map objects
For example, if we add the two objects up above, as first + second, the end result will just be
{settings={exit={differentMessage=message1, secondMessage=message2}}, 2=zebra}
as the exit map in second takes priority over the exit map object in first.

Answer 1

You can try flattening both maps first:
settings.exit.exitMessage=message0
2=2
settings.exit.differentMessage=message1
settings.exit.secondMessage=message2
2=zebra
Then after merging the maps you end up with this:
settings.exit.exitMessage=message0
settings.exit.differentMessage=message1
settings.exit.secondMessage=message2
2=zebra
And then just rebuild the map again by exploding the keys.
Full code sample here: https://pl.kotl.in/p9BaUVOF3
Flattening a map
fun flatten(source: Map<String, Any>, target: HashMap<String, Any>, prefix: String = "") {
for (entry in source) {
var fullKey = if (prefix.length > 0) prefix + "." + entry.key else entry.key
if (entry.value is Map<*, *>) {
flatten(entry.value as Map<String, Any>, target, fullKey)
continue
}
target.put(fullKey, entry.value)
}
}
Exploding a flattened map
fun explode(source: Map<String, Any>, target: HashMap<String, Any>) {
for (entry in source) {
var targetMap = target
var keySegments = entry.key.split(".")
// Rebuild the map
for (keySegment in keySegments.dropLast(1)) {
if (targetMap.containsKey(keySegment)) {
var value = targetMap.get(keySegment)
if (value is Map<*, *>) {
targetMap = value as HashMap<String, Any>
continue
}
}
var newNestedMap = HashMap<String, Any>()
targetMap.put(keySegment, newNestedMap)
targetMap = newNestedMap
}
// Put values into it
targetMap.put(keySegments.last(), entry.value)
}
}