How can I collapse a struct array? - swift

Question

I have a struct for my items:
struct item: Decodable {
var category_id: Int
var name: String
}
Which I'm receiving through JSONDecoder().decode into an array (items: [item]).
And I'd like to collapse it into a structure like this:
struct collapsed{
var category_id = Int()
var items = [String]()
}
So that I can loop through it more conveniently. How can I do that?
So I have this variable:
items: [item]
Which looks like this:
items
[0]
-category_id: 0
-name: "item1"
[1]
-category_id: 1
-name: "item2"
[2]
-category_id: 0
-name: "item3"
[3]
-category_id: 1
-name: "item4"
[4]
-category_id: 0
-name: "item5"
And I want to collapse it to this:
collapseditems: [collapsed]
Which should look something like this:
collapseditems
[0]
-category_id: 0
-items:
[0]: "item1"
[1]: "item3"
[2]: "item5"
[1]
-category_id: 1
-items:
[0]: "item2"
[1]: "item4"

Answer 1

First thing - struct names should start with uppercase letters.
There are a few ways you can translate your array of Item to an array of Collapsed. Here is one approach that first groups the array of Item into a dictionary keyed by category_id. Then that dictionary is mapped into an array of Collapsed. Finally that array is sorted by category_id.
struct Item: Decodable {
var category_id: Int
var name: String
}
struct Collapsed {
let category_id: Int
var items: [String]
}
// Your array of Item - here is some test data
let items: [Item] = [
Item(category_id: 0, name: "item1"),
Item(category_id: 1, name: "item2"),
Item(category_id: 0, name: "item3"),
Item(category_id: 1, name: "item4"),
Item(category_id: 0, name: "item5")
]
// Create a dictionary where the keys are category_id and the values are an array of Item with the same category_id
let mapping = Dictionary(grouping: items, by: { $0.category_id })
// Map that dictionary into an array of Sorted and then sort that array by category_id
let collapsedItems: [Collapsed] = mapping
.map { Collapsed(category_id: $0.key, items: $0.value.map { $0.name }) }
.sorted { $0.category_id < $1.category_id }

Answer 2

You can achieve this by using below code.
var sortedList: [sorted] = []
for i in item {
if let index = sortedList.index(where: { $0.category_id == i.category_id }) {
sortedList[index].items.append(i.name)
} else {
sortedList.append(sorted(category_id: i.category_id, items: [i.name]))
}
}
print(sortedList)

Answer 3

For first question, do you want to make a sorted list of item struct?
If yes, you can use sorted method of Array like this.
let sorted = items.sorted { $0.category_id < $1.category_id }
For Second question, first struct has default value for its properties, but second one hasn't. Second one, therefore, does NOT offer an empty constructor.