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Actually ramda is a better choice if you want FP because everything is auto-curried by default and the argument order makes the curried functions a bit more useful:

http://ramda.github.io/ramdocs/docs/

I think Lo-Dash is a better alternative.

Not trying to start a flamewar, but are there instances where you would use underscore instead of lodash?

yes, for example, https://github.com/documentcloud/underscore-contrib

You could theoretically use this on top of lodash though, correct?

There's lodash-contrib too – https://github.com/TheNodeILs/lodash-contrib

To be more explicit. Underscore is a great library and it let's you use functional programming concepts on collections. However, RX is about unifing that use to streams and more familiar events.

Summary: I wouldn't skip this great tutorial because you've used Underscore and think some of these concepts are similar.