[ITLib] Get a tree of artists / albums (Mac OS Swift app)

On line 3 you build a list of artist names and then on line 4 you iterate that list and on line 5 you filter the tracks to find the tracks for that artist. But you’ve already gone through the list of tracks on line 3, so you can accumulate the info you need at that point. For example, in the code below I walk the list of tracks building a dictionary that maps the artist name to a list of their tracks.

struct Track {
    var id: Int
    var artist: String
}

let tracks = [
    Track(id: 1, artist: "a"),
    Track(id: 2, artist: "b"),
    Track(id: 3, artist: "c"),
    Track(id: 4, artist: "a"),
    Track(id: 5, artist: "a"),
    Track(id: 6, artist: "a"),
    Track(id: 7, artist: "b"),
]
let tracksByArtist = Dictionary(grouping: tracks, by: { $0.artist })
for (artist, tracks) in tracksByArtist {
    print(artist, tracks.map { $0.id })
}
// prints:
//
// a [1, 4, 5, 6]
// b [2, 7]
// c [3]

There’s probably a bunch of other things you can improve here, but let’s stack with this.

Share and Enjoy
—
Quinn “The Eskimo!”
Apple Developer Relations, Developer Technical Support, Core OS/Hardware

let myEmail = "eskimo" + "1" + "@apple.com"

There is something I don't understand in your code:

Line 2, you create an empty array

    var theArtists: [Artist] = [Artist]() // just a custon obj to record the artists

You return the array on line 27

    return theArtists

But it was never modified in between.

So either it is useless, or your code cannot work.

Did I miss something ?

2 years ago, I'm back on this post !

I think my approach is too complicated even if it is working...

Like Eskimo said, Dictionary seems to be the key but I'm not familiar with that to manipulate arrays...

Do I need to do multiple dictionary of can I have all my structure in only one ?

Thx.

Hi,

In fact, I'd like to reproduce what we have in the Music app :

The Eskimo's way with the Dictionary seams to be great but I need to have the Artist >>> Albums >>> Tracks schema.

Thx for your help.

Hi,

So thanks to Eskimo and his group by trick (very useful), I just finished a pretty good version of my artists - albums - tracks tree.

Here is my playground :

import Cocoa
import iTunesLibrary

do {
    let lib = try ITLibrary(apiVersion: "1.1")
    let theITTracks = lib.allMediaItems.filter({$0.mediaKind == .kindSong})
    
    let theTracksByArtist = Dictionary(grouping: theITTracks, by: { $0.artist?.name } )
    
    var theArtistsTree = [Artist]()
    for(artistKey, tracksByArtist) in theTracksByArtist {
        print("artistKey >>>", artistKey)
        print("/////////")
        let theAlbumsTracks = tracksByArtist.map{ $0 }
        let theITArtist = theAlbumsTracks.first?.artist
        let theArtist = Artist(theITArtist: theITArtist!)
        
        let theArtistAlbums = Dictionary(grouping: theAlbumsTracks, by: { $0.album.persistentID } )
        for (albumID, tracksAlbum) in theArtistAlbums {
            let theTracksAlbum = tracksAlbum.map { $0 }
            let theITAlbum = theTracksAlbum.first?.album
            let theAlbum = Album(theITAlbum: theITAlbum!)
            
            print(theTracksAlbum.first?.album.title)
            print("++++")
            
            for track in theTracksAlbum {
                print(track.title)
                let theTrack = Track(theITTrack: track)
                theAlbum.tracks.append(theTrack)
            }
            print("***************")
            
            theArtist.albums.append(theAlbum)
        }
        
        theArtistsTree.append(theArtist)
        print("---------------------------------------------------------------------------------------------------")
    }
    
} catch let error {
    print(error)
}

But I have a bunch of problems to solve like the sort of the dictionary grouped by artist.

I tried :

let theTracksByArtist = Dictionary(grouping: theITTracks, by: { ($0.artist?.name)! } ).sorted(by: { $0.key.localizedStandardCompare($1.key) == .orderedAscending })

It is working until the moment an artist nil is parsed :

Multiline error: Execution was interrupted, reason: EXC_BREAKPOINT (code=1, subcode=0x1006c2ad8). The process has been left at the point where it was interrupted, use "thread return -x" to return to the state before expression evaluation.

So how to avoid this error ? Do I need to test the artist?.name before to compare it ? How to ?

Thx.

What about writing

($0.artist?.name) ?? "--"

I tried :

let theTracksByArtist = Dictionary(grouping: theITTracks, by: { $0.artist?.name ?? "--" } ).sorted(by: { $0.key.localizedStandardCompare($1.key) == .orderedAscending })

And it is working, thx !

What is "--" ? Special code or can I type "" ?

What is "--" ? Special code or can I type "" ?

Just a pseudo name, to avoid an empty string. You may filter them out after.

Did you try ? Does it solves the crash ?

Hi,

Another problem here is when I get all the tracks artist's albums, the function is slow :

for track in theTracksAlbum {
                print(track.title)
                let theTrack = Track(theITTrack: track) // a NSObject to show it in a NSOutlineView
                theAlbum.tracks.append(theTrack)
            }

If I comment those lines, the tree appears instantly.

Problem : I need the albums tracks to get the artwork's album (right ?) and especially to add them in a playlist.

So each time I click on an artist, I could execute a function to retrieve all the tracks albums, it is not so difficult.

But before to do that, I'd like to know if I could enhance something to get the tracks ? Each time I do a loop to build objects, the program goes slow...

I think it is possible because when I click on the Artists / All artists in the Music app, it is fast :

Thx.

Hi,

No answer but for those like me who have this problem, I solved it.

As I don't need to show the tracks in the NSOutlineView :

I add directly the ITTracks to an array in the album :

for (albumID, tracksAlbum) in theArtistAlbums {
                let theTracksAlbum = tracksAlbum.map { $0 }.sorted(by: { $0.trackNumber < $1.trackNumber })
                let theITAlbum = theTracksAlbum.first?.album
                let theAlbum = Album(theITAlbum: theITAlbum!)
                theAlbum.ITTracks = theTracksAlbum // tracks added here, don't need to build a NSObject in the loop like before...
                
                theArtist.albums.append(theAlbum)
            }

The powerful way here is to use the map of tracksAlbum.map.

But for my info, is it possible to build objects in this kind of function instead of doing a loop like I tried to do which is very slow ?

Thx.