Combine CF method

[howeverforever]

I don't know how useful it is. But we need a try.

[ctjoy]

In my case, using CF is still useful. It improved my score about 0.02% in the test dataset. On the other hand, it improved the AUC score 0.71 to 0.84 in the validation dataset. I think the main problem on this issue is cold start. You can see further information on this thread: https://www.kaggle.com/c/kkbox-music-recommendation-challenge/discussion/42795