Filter to get List of data at particular category

Android
1

Hey, I have a JSON response and i need to filter that data in a list. In every JSONObject there are 3 categories in which only one category holds data.

data class CategoryResponse(
        val item: List<CategoryItem>
)
data class CategoryItem(
        val id: Int,
        val Category1: List<ItemOptions>? = null,
        val Category2: List<ItemOptions>? = null,
        val Category3: List<ItemOptions>? = null
)
data class ItemOptions(
        val name: String? = null,
        val url: String? = null
)

I have an enum class, which has 4 enum types

enum class CategoryType(val name :String){
  ALL("ALL"),
  Category1("Category1"),
  Category2("Category2"),
  Category3("Category3");
}

There is a category named ALL, so i need the list of all the data but I don’t want any null values, and still want the data that other categories hold.
Example - the list consist of 5 elements
Desired output:
ALL : list-> [id : 1 , category1 : ”…”] , [id : 2 ,category2 : “…”] , [id : 3 ,category2 : ”…”] , [id : 4 ,category1 : “…”] , [id : 5 ,category3: “…"]

CATEGORY2: list → [id : 2 , category2 : “…”] , [id : 3 , category2 : “…”]
(this list may or may not consist of more than 5 elements)
is there any way that this list won’t occupy a lot of memory, or duplicate the objects and could be more efficient.?

{
	"items": [{
		"id": "1",
		"Category1": [{
			"name": "Item ..",
			"url": "https:..."
		}, {
			"name": "Item ..",
			"url": "https:..."
		}],
		"Category2": [],
		"Category3": []
	}, {
		"id": "2",
		"Category1": [],
		"Category2": [{
			"name": "Item ..",
			"url": "https:..."
		}],
		"Category3": []
	}, {
		"id": "3",
		"Category1": [],
		"Category2": [{
			"name": "Item ..",
			"url": "https:..."
		}],
		"Category3": []
	}, {
		"id": "4",
		"Category1": [{
			"name": "Item ..",
			"url": "https:..."
		}],
		"Category2": [],
		"Category3": []
	},{
		"id": "5",
		"Category1": [],
		"Category2": [],
		"Category3": [{
			"name": "Item ..",
			"url": "https:..."
		}]
	} ....]
}