Merge properties of a list to another based on properties objects - kotlin

Question

I got 2 lists with x objects inside , for example:
data class Model(
var token: String = "",
var id: String = "",
var name: String = "",
var image: Int = 0,
)
array is initialized and filled, the other list has x objects also that contains the objects of the first list but with different values in their properties!
what I want to do is to change the properties of the first array by the second one if they got the same object.name
var arr1 = ArrayList<Model>() // locale
var arr2 = ArrayList<Model>() // from db
the first array I got for example
[Model(name = "David", token = "" , image = 0)]
the second array I got
[Model(name = "David", token = "1asd5asdd851", image = 1)]
How do I make the first array take the missing token?
I tried with .filter{} and with .map{}. groupBy {} for hours because Name is the only properties that are the same but I'm more and more confused.

Answer 1

We can first group the second array by name using associateBy() and then iterate over first array and reassign properties:
val arr2ByName = arr2.associateBy { it.name }
arr1.forEach { item1 ->
arr2ByName[item1.name]?.let { item2 ->
item1.token = item2.token
item1.image = item2.image
}
}
Alternatively, if you don't need to modify items in arr1, but create another array and you can use items from both arr1 and arr2, then it will be much easier:
val arr3 = arr1.map { arr2ByName[it.name] ?: it }

Answer 2

One possible way would be to use fold() as follows:
fun main(args: Array<String>) {
val arr1 = listOf(Model(name = "David", token = "" , image = 0))
val arr2 = listOf(Model(name = "David", token = "1asd5asdd851", image = 1))
val mergedModels = arr2.fold(arr1) { localModels, dbModel ->
localModels.map { localModel ->
if (localModel.name == dbModel.name) localModel.copy(token = dbModel.token, image = dbModel.image)
else localModel
}
}
println(mergedModels)
}
If you want to reuse arr1 variable then you can do the following (but I would still use the previous option):
fun main(args: Array<String>) {
var arr1 = listOf(Model(name = "David", token = "" , image = 0))
val arr2 = listOf(Model(name = "David", token = "1asd5asdd851", image = 1))
arr1 = arr2.fold(arr1) { localModels, dbModel ->
localModels.map { localModel ->
if (localModel.name == dbModel.name) localModel.copy(token = dbModel.token, image = dbModel.image)
else localModel
}
}
println(arr1)
}