How to sum the Value from the same Key using a Dictionary? - swift

Question

I have a dictionary the looks like this:
(value: 21.0, id: "JdknnhshyrY56AXQcAiLcYtbVlz2") ---> This has a second entry
(value: 18.0, id: "nIvb519nNfMtlVNnsQJ5w4bRbFp2")
(value: 14.0, id: "tlKqcxHdPoemwGqJsyLhERnuQ3Z2")
(value: 5.0, id: "JdknnhshyrY56AXQcAiLcYtbVlz2")]---> This is the second entry
I want to add the value to the same id if has a duplicate entry.
Something like this:
(value: 26.0, id: "JdknnhshyrY56AXQcAiLcYtbVlz2") ---> Value has added and key has become only one
(value: 18.0, id: "nIvb519nNfMtlVNnsQJ5w4bRbFp2")
(value: 14.0, id: "tlKqcxHdPoemwGqJsyLhERnuQ3Z2")]
I already tried using a map method but has been working, has added the values but still multiple entries on the id keeping more than one.
How can I achieve the result.

Answer 1

It's always advisable to convert your Dictionary (with heterogeneous
type of values that eventually falls into [AnyHashable : Any]
category) to a Typed object. With typed object, manipulation or
other calculation become handy.
On the premise of the above statement you will do something like:
let objects = [Object]() // this would be you array with actual data
let reduced = objects.reduce(into: [Object]()) { (accumulator, object) in
if let index = accumulator.firstIndex(where: { $0.id == object.id }) {
accumulator[index].value += object.value
} else {
accumulator.append(object)
}
}
Where the Object is:
struct Object {
var value: Double
let id: String
}
Now if you are wondering how would you convert your Dictionary to & from Object type, look at the complete code:
let arrayOfDictionary = [["value": 21.0, "id": "JdknnhshyrY56AXQcAiLcYtbVlz2"],
["value": 18.0, "id": "nIvb519nNfMtlVNnsQJ5w4bRbFp2"],
["value": 14.0, "id": "tlKqcxHdPoemwGqJsyLhERnuQ3Z2"],
["value": 5.0, "id": "JdknnhshyrY56AXQcAiLcYtbVlz2"]]
struct Object: Codable {
var value: Double
let id: String
}
do {
let jsonData = try JSONSerialization.data(withJSONObject: arrayOfDictionary, options: [])
let objects = try JSONDecoder().decode([Object].self, from: jsonData)
let reduced = objects.reduce(into: [Object]()) { (accumulator, object) in
if let index = accumulator.firstIndex(where: { $0.id == object.id }) {
accumulator[index].value += object.value
} else {
accumulator.append(object)
}
}
let encodedObjects = try JSONEncoder().encode(reduced)
let json = try JSONSerialization.jsonObject(with: encodedObjects, options: [])
if let reducedArrayOfDictionary = json as? [[String : Any]] {
print(reducedArrayOfDictionary)
}
} catch {
print(error)
}