Add address book like letters in array of names

Question

I'm trying to take an array of people (simplified with just a first name for now) and not only sort it, but also add the first letter in front of all people starting with this letter.

Basically this: ["Daniel", "Michael", "Lisa", "Lena"] should become this: ["D", "Daniel", "L", "Lena", "Lisa", "M", "Michael"]

I have something working in a playground, but to me this looks ugly as hell and no idea about performance if people get in the thousands or more.

//: Playground - noun: a place where people can play

import Cocoa

var previousName: String?

let people = ["Martin", "Michael", "Lisa", "Lena", "Dirk"]
var peopleWithLetters: [String] = []

people.sorted { $0.localizedCaseInsensitiveCompare($1) == ComparisonResult.orderedAscending }.forEach {
    if $0.uppercased().characters.first! != previousName?.uppercased().characters.first! {
        peopleWithLetters.append("\($0.uppercased().characters.first!)")
    }
    previousName = $0
    peopleWithLetters.append($0)
}

Any idea how to streamline or follow best practices would be highly appreciated.

Answer 1

This is a perfect usecase where functional programming shines.

• Map array of names to array of first letters
• Use a set to remove duplicates
• Combine letters with names
• Sort the array

Here is the code:

//: Playground - noun: a place where people can play

func addSections(in words: [String]) -> [String] {
    let sections = Set(words.map { String($0[$0.startIndex]) })
    let wordsWithSections = words + sections
    return wordsWithSections.sorted { $0 < $1 }
}

let names = ["Daniel", "Michael", "Lisa", "Lena"]
addSections(in: names)

Although if you plan on using this array to feed a tableView (sections/rows) you would be better off with a dictionary like you mentioned in your comment.