538 did something interesting - they applied Latent semantic analysis to Reddit, to see where else Reddit's trump-supporting population falls in terms of other subreddits.
The entire thing is worth reading, but some interesting(and in hindsight, pretty obvious) takeaways:
The_Donald + Games = KotakuInAction(Gamergate sub), /r/gaming(The largest gaming sub, which is often pretty much reddit standard right-wing), and /r/cynicalbrit(The subreddit for gamergate favorite youtuber TotalBiscuit)
/r/conservative - /r/politics = Three catholic subreddits, one general christian subreddit, and one dedicated to AK47s.
The_Donald - Politics = /r/fatpeoplehate(now banned subreddit, what it says on the tin), TheRedPill(Reddit's MRA community hub), the 4chan sub, and an explicitly racist sub.
Oh, and they also threw their code for the project up on Github, and pointed to where they got their raw data from(Google's BigQuery)