Categorize: Function returns a double

[isaacsanders]

The specification states that the function passed to Categorize, quantity, takes a data point and returns a double. I feel like a more appropriate name may be category, as well as the correction that it should return a string.

Source

[jpivarski]

That's a copy-paste error. The function accepted by Categorize takes a function that returns a string. The Scala implementation is explicit about that.

[jpivarski]

Fixed.