Group by an object in an array - ios

Question

I have two objects. One called EstimateItem and the other one is called Part (Part class is inherited from Realm's Object class). One EstimateItem can have multiple Parts.
class EstimateItem {
var parts: [Part]?
}
There's an array of EstimateItems with different numbers of Parts in each instance.
+--------------------------------+---------------------------------+
| EstimateItem | Parts |
+--------------------------------+---------------------------------+
| Line Item 1 - RnR WDH - Twins | Epoxy / Wood for lami |
| (single) | |
| | |
| Line Item 2 - RnR WDH - Twins | Epoxy / Wood for lami |
| (double) | |
| | |
|Line Item 3 - Install sash lock |Epoxy / Wood for lami / Sash lock|
+--------------------------------+---------------------------------+
I need to group them by specific Part. It should look something like this.
How do I do this?
I couldn't figure out a way to do this while the parts are attached to individual item so I tried laying them all out in an array of (part: Part, item: EstimateItem) tuples.
var groups = [(part: Part, item: EstimateItem)]()
for item in estimateItemsArray {
if let parts = item.parts {
for part in parts {
groups.append((part, item))
}
}
}
// Epoxy - RnR WDH - Twins (single)
// Wood for lami - RnR WDH - Twins (single)
// Epoxy - RnR WDH - Twins (double)
// Wood for lami - RnR WDH - Twins (double)
// Epoxy - RnR WDH - Twins (single)
// Wood for lami - RnR WDH - Twins (single)
// Sash lock, traditional - Install sash lock
And then group it.
But I'm still stuck. Also I feel like I'm overcomplicating it and I was wondering if there's an easier and more Swifty way of doing this.

Answer 1

What I came up with trying to find a more swifty way of doing this is the following:
let parts = Set(estimateItemsArray.flatMap{ $0.parts ?? [] })
let partMap = parts.map { part in
return (part, estimateItemsArray.filter {
$0.parts?.indexOf(part) != nil
}
)
}
partMap now contains tuples of the form (Part, [EstimateItem]). The only requirement is for Part to conform to Hashable or something related - in my test I just let Part inherit from NSObject.
Explanation:
create an array of all the available parts (Set to ensure uniqueness)
loop over the array mapping and returning a tuple of
the actual part
loop over estimateItemsArray filtering out the items that have the current part in their list
The complete test-data looks like this
/* the now classes, both include some identifier to distinguish them */
class Item {
var n : String
var parts : [Part]? = [Part]()
init(n:String) {
self.n = n
}
}
class Part : NSObject {
var n : String
init(n:String) {
self.n = n
}
}
/* set up the test data */
let item1 = Item(n: "item 1")
let item2 = Item(n: "item 2")
let item3 = Item(n: "item 3")
let part1 = Part(n: "part 1")
let part2 = Part(n: "part 2")
let part3 = Part(n: "part 3")
item1.parts = [part1, part2]
item2.parts = [part1, part3]
item3.parts = [part1, part2, part3]
var arrItems = [item1, item2, item3]
/* actual logic */
let parts = Set(arrItems.flatMap{ $0.parts ?? [] })
let partMap = parts.map { part in
return (part, arrItems.filter {
$0.parts?.indexOf(part) != nil
}
)
}
/* final output */
partMap.forEach { entry in
print("part \(entry.0.n)")
entry.1.forEach {
print("contains \($0.n)")
}
}
Outputting:
part part 1
contains item 1
contains item 2
contains item 3
part part 3
contains item 2
contains item 3
part part 2
contains item 1
contains item 3
If you cannot inherit from NSObject like I initially though, make your class Part conform to Hashable which is the requirement for sets:
class Part : Hashable {
var n : String
init(n:String) {
self.n = n
}
var hashValue: Int {
return n.hashValue // you basically have to provide some kind of logic based on *your* Part object
}
}
func ==(lhs: Part, rhs: Part) -> Bool {
return lhs.hashValue == rhs.hashValue
}