Making sections for a 2D array to be used in a CollectionView or TableView. [Fellow] => [[Fellow]]

MakingSectionsFromArray.swift

// Making sections for a 2D array to be used in a CollectionView or TableView. [Fellow] => [[Fellow]]

import Foundation

struct Fellow {
  let name: String
  let cohort: String
  
  static func allFellows() -> [Fellow] {
    return [
      Fellow(name: "Kim", cohort: "data science"),
      Fellow(name: "Herb", cohort: "data science"),
      Fellow(name: "Sandy", cohort: "web"),
      Fellow(name: "James", cohort: "web"),
      Fellow(name: "Bob", cohort: "web"),
      Fellow(name: "Al", cohort: "iOS"),
      Fellow(name: "Cindy", cohort: "android"),
      Fellow(name: "Yi", cohort: "android"),
      Fellow(name: "Malik", cohort: "iOS"),
      Fellow(name: "Nancy", cohort: "web"),
      Fellow(name: "Xavier", cohort: "iOS"),
      Fellow(name: "William", cohort: "android"),
    ]
  }
}

extension Fellow {
  static func makeSections(from fellows: [Fellow]) -> [[Fellow]] {
    // 1
    // first make sure the collection is sorted using the section property you're interested in using e.g by season if working with a TV show model
    let sortedFellows = fellows.sorted { $0.cohort < $1.cohort } // O(n log n)
    
    // 2
    // get the first sorted cohort, this will be the section name
    guard var currentCohort = sortedFellows.first?.cohort else { return [] }
    
    // 3
    // make over the section name and get a unique collection using Set
    let cohorts = Set(fellows.map { $0.cohort }) // O(n)
    
    // 4
    // create an empty 2-D Array [[Fellow]], this will be the sections to be used in a table view or collection view's sections
    var sections = Array(repeating: [Fellow](), count: cohorts.count)
    
    // 5
    // declare a property currentIndex and assign it zero since we are starting to populate the array from index 0
    var currentIndex = 0
    
    // 6
    // iterate through the given array
    for fellow in sortedFellows { // O(n)
      // 7
      // if we are not looking athe the current section (cohort) then
      if fellow.cohort != currentCohort {
        // 8
        // increment the currentIndex so we are starting to populate a new section with the array
        currentIndex += 1
        // 9
        // update the current section name (cohort)
        currentCohort = fellow.cohort
      }
      // 10
      // append the current item (fellow) to the array withing the current section
      sections[currentIndex].append(fellow)
    }
    // 11
    // we now have an array or arrays and are ready to populate our table view or collection view
    return sections
  }
} // complexity: O(n log n) if we have to sort the collection, if the collection is already sorted it will be O(n)

let allFellows = Fellow.allFellows() // [Fellow] - one dimentional array
let sections = Fellow.makeSections(from: allFellows) // [[Fellow]] - two-dimensional array
dump(sections)

/*
 ▿ 4 elements
 ▿ 3 elements
   ▿ __lldb_expr_27.Fellow
     - name: "Cindy"
     - cohort: "android"
   ▿ __lldb_expr_27.Fellow
     - name: "Yi"
     - cohort: "android"
   ▿ __lldb_expr_27.Fellow
     - name: "William"
     - cohort: "android"
 ▿ 2 elements
   ▿ __lldb_expr_27.Fellow
     - name: "Kim"
     - cohort: "data science"
   ▿ __lldb_expr_27.Fellow
     - name: "Herb"
     - cohort: "data science"
 ▿ 3 elements
   ▿ __lldb_expr_27.Fellow
     - name: "Al"
     - cohort: "iOS"
   ▿ __lldb_expr_27.Fellow
     - name: "Malik"
     - cohort: "iOS"
   ▿ __lldb_expr_27.Fellow
     - name: "Xavier"
     - cohort: "iOS"
 ▿ 4 elements
   ▿ __lldb_expr_27.Fellow
     - name: "Sandy"
     - cohort: "web"
   ▿ __lldb_expr_27.Fellow
     - name: "James"
     - cohort: "web"
   ▿ __lldb_expr_27.Fellow
     - name: "Bob"
     - cohort: "web"
   ▿ __lldb_expr_27.Fellow
     - name: "Nancy"
     - cohort: "web"
*/