Ttykuu

I want to group an array of structs only using arrays into an array of new structs. In this example I want to group the Person structs by Job and put them in new Department structs and put them in an array.

enum Job 
 case developer
 case programmer
 case coder


struct Person 
 let id: Int
 let job: Job 


struct Department 
 let job: Job
 var staff: [Person]

 mutating func addStaff(_ person: Person) 
 staff.append(person)
 


let initial = [
 Person(id: 0, job: .developer),
 Person(id: 1, job: .developer),
 Person(id: 2, job: .programmer),
 Person(id: 3, job: .programmer),
 Person(id: 4, job: .coder)
]

func combinator(accumulator: [Department], current: Person) -> [Department] 
 var accumulator = accumulator

 if let index = accumulator.index(where: $0.job == current.job ) 

 var department = accumulator[index]
 department.staff.append(current)
 accumulator[index] = department
 else 
 accumulator.append(Department(job: current.job, staff: [current]))
 

 return accumulator


var departments: [Department] = initial.reduce([], combinator)

I feel like the if statement in the combinator(accumulator:current:) function is a bit clunky, is there a better way to write that part or any other part of this piece of code?

Swift 4

i would use the new swift 4 init(grouping:by:)

since you create always new Departments then the following code is possible.

if you have an existing [Department] then the code not fit your request.

enum Job 
 case developer
 case programmer
 case coder


struct Person 
 let id: Int
 let job: Job 


struct Department 
 let job: Job
 var staff: [Person]

 mutating func addStaff(_ person: Person) 
 staff.append(person)
 


let initial = [
 Person(id: 0, job: .developer),
 Person(id: 1, job: .developer),
 Person(id: 2, job: .programmer),
 Person(id: 3, job: .programmer),
 Person(id: 4, job: .coder)
]

let grouped = Dictionary(grouping: initial, by: $0.job )
let departments = grouped.map key, value in Department( job: key, staff: value )

( NOTE: i don't tested it in playground - just from head to the answer)

Swift 3

in Swift 3 you can use an extension to the array to resolve this grouping

public extension Sequence 
 func group<U: Hashable>(by key: (Iterator.Element) -> U) -> [U:[Iterator.Element]] 
 var categories: [U: [Iterator.Element]] = [:]
 for element in self 
 let key = key(element)
 if case nil = categories[key]?.append(element) 
 categories[key] = [element]
 
 
 return categories
 

the extension is from here https://stackoverflow.com/a/31220067/1930509 and when you need a more performat grouping you can find it at the link