I was searching for it because I wanted to start doing posts like, "10 most active discussions on Steemit for you to get involved in right now" for people that like discussions as much as I do.
I had no luck finding a way to filter post results by comments though. I was a little surprised. You can do so much with some of these tools, and arranging posts by comments sounds like a much more simple thing than all the complex analytical tools available.