Populate UITableView with Sections - arrays

Question

I'm trying to populate TableView with sections. Where an artist is the Section Name and all songs of that artist are listed below. In total over 100 artists. Like so
FirstArtist
- Song 1
- Song 2
SecondArtist
- Song 1
- Song 2
OneMoreArtist...
I have an array of objects Song
struct Song {
let songName: String?
let album: String?
let artist: String?
}
var songs = [Song]()
And an array of all artists names
var artists = [String]()
As I understand, to populate tableView with sections I need a Dictionary with Artist as key and array of Songs as value, like so
var toShow = [String : [Song]]()
So, then I'm trying to loop
for artist in artists {
for song in songs {
if song.artist == artist {
toShow[artist] = [song]
// toShow[artist]?.append(song)
}
}
}
But it doesn't work.
Probably I'm going wrong way.
What is the solution in this situation?
Thanks
Update
Made a stuct
struct ArtistWithSongs {
let name: String
let songs: [Song]
init(name: String, songs: [Song]) {
self.name = name
self.songs = songs
}
}
and trying to loop
var artistWithSongs = [ArtistWithSongs]()
for artist in artists {
for song in songs {
if artist == song.artist {
artistWithSongs.append(ArtistWithSongs(name: song, songs: [song]))
}
}
}
But apparently, my variant of looping is not correct. Now I'm getting an array of objects contains duplicate keys and only one Song per Key. It looks like
[Atrist1 : [Song1], Artist1 : [Song2], Artist1 : [Song3], ...]
My question is - What is the right way to make a loop, or is it possible somehow to merge objects with an identical key inside a Dictionary to get this [Artist1 :[Song1, Song2, Song3]]?

Answer 1

Thanks to everyone, I found a solution here, it worked for what I was trying to achieve. Roughly like this
let toShow = artistWithSongs.reduce([ArtistWithSongs](), { partialResult, artist in
var dupe = partialResult.filter {$0.songName == group.name }.first
if let dupeArtist = dupe {
dupeArtist.songs?.append(contentsOf: artist.songs ?? [])
return partialResult
} else {
var newPartialResult = partialResult
newPartialResult.append(group)
return newPartialResult
}
})

Answer 2

In addition to your Song struct
struct Song {
let songName: String?
let album: String?
}
create Artist one like
struct Artist {
let name:String
let songs = [Song]()
}
Then create an array of them
var artists = [Artist]()
let s1 = Song(songName:"name1",album:"alb1")
let s2 = Song(songName:"name2",album:"alb2")
let artist1 = Artist(name:"art",songs:[s1,s2])
artists.append(artist1)
In numberOfSections return
artists.count
In numberOfRows return
artists[section].songs.count
In cellForRowAt access
let song = artists[indexPath.section].songs[indexPath.row]

Answer 3

If you want to transform an array of songs ([Song]) to a dictionary ([String : [Song]]), I would recommend using functional style:
self.toShow = songs.reduce([String: [Song]]()) { acc, next in
// mutable copy
var acc = acc
// since artist is optional we need to substitute it with non-optional value if it's nil
let artist = next.artist ?? "Unknown Artist"
// if dictionary already has this artist, then append the `next` song to an array
if acc[artist] != nil {
acc[artist]?.append(next)
} else {
// otherwise create new array
acc[artist] = [next]
}
return acc
}
In your table's data source provide the number of sections:
func numberOfSections(in tableView: UITableView) -> Int {
return self.toShow.keys.count
}
And then you'll face a trouble: for number of rows in section you'll need to know which artist is the section stands for. So, I suggest you to use one more structure, an array of artists so that you keep the order of sections consistent:
self.artists = Array(self.toShow.keys).sorted()
This way, you can provide your table with following numbers of sections and rows:
func numberOfSections(in tableView: UITableView) -> Int {
return self.artists.count
}
func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
let artist = self.artists[section] // get the artist's name
return self.toShow[artist]?.count ?? 0
}