How I Use the Last.fm API

I've integrated the Last.fm API into my website so that I can listen to an album, scrobble it, and expect a link to show up on my website for the next few days.

I call the user.getTopAlbums method and query for the most played albums over the last seven days. If I listen to a new album, then it jumps to the top of the list and stays there for a week. Alternatively, if I shuffle a playlist, then different albums trade places between the middle and end of the list. I also limit the number of results to a Top 50.

However, if two albums have the same number of plays (over the past week), then Last.fm sorts them by the artist name. This poses a problem, since my recently played albums typically taper off in playcount, such that all albums ranking below #20 or #30 have only one play. Therefore, if I listen to a bunch of different songs from a bunch of different albums, then albums by artists whose names are sorted last alphabetically might not even make it on the list.

In this blog post, I'll go over how I get around this limitation and implement a recent top albums list that uses my recently played songs to order albums with the same number of plays.

Step 1: Define the Problem

It's often wise to establish boundaries before implementing something so that you have a clear focus on what to work on. The issue at hand is that I want to resort the data returned from user.getTopAlbums so that albums with the same playcounts are resorted according to the most recently played tracks from each album.

I imposed the following limits on how complicated my solution could become:

• I would make at most one additional call to the Last.fm API.

• Consequently, the result might not be perfect. If I scrobble a large number of songs from different albums in a short period of time, then I might not get enough data to obtain the ideally perfect reordered list.

• Finally, I will not try to solve a different problem, namely that scrobbles on compilation albums aren't grouped together into a single album. (I had to change my mind and no longer think of this as a problem. 😃)

Step 2: Get Recent Tracks

The other API method I use is user.getRecentTracks, which I can query over the same seven day period as I use for user.getTopAlbums. I also set the result limit to the maximum of two hundred items, and I increase the limit for user.getTopAlbums to one hundred, slicing it to the top fifty after performing my own sorting algorithm.

Step 3: Reduce Recent Tracks to Recent Albums

The data returned from user.getRecentTracks includes the album name for each track. Therefore, we can reduce this list to just albums names.

To be clear, I am transforming an array of data objects to an array of strings. Here is the code I use, where recentTracks is the variable name for the Last.fm API response object.

const recentAlbumNames = recentTracks.recenttracks.track.reduce(
  // The reduce function builds a return value
  // by iterating on each element of an array.
  //
  // Here, we are iterating over a list of tracks
  // that are already sorted by most recently played.
  (albums: string[], track) => {
    if (albums.includes(track.album["#text"])) {
      return albums;
    }
    // Add a newly found album to the running list.
    albums.push(track.album["#text"]);
    return albums;
  },
  [], // Start with an empty list.
);

Step 4: Re-sort Top Albums

Finally, I re-sort the list of top albums according to the following rules:

1. If two albums have different playcounts, then sort them normally, by their playcounts.

2. Otherwise, then we resort ‒ that is, fallback ‒ to the reduced recentAlbumNames array computed earlier.

   1. If two albums are each in the recentAlbumNames list, then we can sort them according to their order in that list.

   2. If only one album is in the list, then we sort that one higher, because it was listened to more recently.

   3. If neither album was listened to recently, then we can sort them by their album name.

This is the new "Top Albums" list, and I finish off by slicing the first fifty items for use in my website's homepage.