Oops. I missed that `r.row` wasn't there in that API. So would the Ruby version would be more like:

```rb
r.table("users").index_create("activities", :multi => true){ |activity|
    activity["hobbies"] + activity["sports"]
}.run(conn)
```

(I used `r.add` because it was in the compound index example above; couldn't that also be rewritten with `+`, if it's just doing string concatenation, or am I missing something subtle about `r.add`?)