Ask HN: What toy project would you recommend to learn ML?

Go to Kaggle.com and use the "contests" that are always running, and intended to serve as introductory tutorials. The "Titanic" one is pretty much the "hello, world" of Machine Learning.

Building an MNIST hand-written digit recognizer is also kindof "hello world"'ish in the ML world.

Also, the various exercises in "Hands-on Machine Learning with Sci-kit Learn and Tensorflow" are good. Note that there's a newer version of the book that's either out or coming out Real Soon Now that changes the title slightly. I think now it also mentions Keras.

I'm interested in this as well. Hopefully we'll see some good answers here.