{"id":2081,"date":"2018-04-08T07:49:37","date_gmt":"2018-04-08T06:49:37","guid":{"rendered":"http:\/\/www.andrewj.com\/blog\/?p=2081"},"modified":"2018-04-08T08:16:01","modified_gmt":"2018-04-08T07:16:01","slug":"inferring-algorithms-how-random-is-your-music-player","status":"publish","type":"post","link":"https:\/\/www.andrewj.com\/blog\/2018\/inferring-algorithms-how-random-is-your-music-player\/","title":{"rendered":"Inferring Algorithms: How Random is Your Music Player?"},"content":{"rendered":"

“You’re Inferring that I’m stupid.”<\/em><\/p>\n

“No, I’m implying that you’re stupid. You’re inferring it.”<\/em><\/p>\n

– Wilt, by Tom Sharpe<\/em><\/p>\n

My latest contract means spending some time on a bus at each end of the day. The movement of the bus means it’s not comfortable to read, so I treated myself to a nearly new pair of decent BlueTooth headphones, and rediscovered the joys of just listening to music. I set the default music player app to “random” and let it do its stuff.<\/p>\n

That’s when the trouble started. I started thinking about the randomisation algorithm used by the music player on the Sony phone. I can’t help it. I’m a software architect – it’s what I do.<\/p>\n

One good music randomisation algorithm would look like this:<\/p>\n

    \n
  1. Assign every song on your device a number from 1 to n<\/li>\n
  2. When you want to play a random song, generate a random number between 1 and n, and play the song with that number.<\/li>\n<\/ol>\n

    However in my experience no-one ever implements this, as it relies on maintaining an index of all the music on the device, and assigning sequential numbers to it. That’s not actually very difficult, given that every platform indexes the music anyway and a developer can usually access that data, but it’s not the path of least resistance.<\/p>\n

    Let’s also say a word about generating random numbers. In reality these are always pseudo-random, and depending on how you seed the generator the values may be predictable. That may be the case with Microsoft’s software for picking desktop backgrounds, which seems to pick the same picture simultaneously on my laptop and desktop more often than I’d expect, but that’s a topic for another blog, so for now let’s assume that we can generate an acceptably random spread of pseudo-random numbers in a given integer range.<\/p>\n

    Here’s another algorithm:<\/p>\n

      \n
    1. Start in the top directory for the music files<\/li>\n
    2. Pick an item from that directory at random. Depending on the type:\n