So I have a map like this: {"2018-05-22" {:A {123 "foo"}}}. I need to transform "foo", but I need to collect some of the map keys (`"2018-05-22"` and :A) along the way for the transformation function and I can't quite figure out how to do it.

@flowthing How do you need to navigate to "foo"? Recursively?

With MAP-VALS. Basically, I'm doing something like this:

(specter/transform [specter/MAP-VALS specter/MAP-VALS specter/MAP-VALS] (fn [& args] ,,,) {"2018-05-22" {:A {123 "foo"}}})

@flowthing yes, you want to make use of collection navigators

(def MAP-VALS+ (path ALL (collect-one FIRST) LAST))
(transform [MAP-VALS+ MAP-VALS+ MAP-VALS]
  (fn [k1 k2 v]
    [k1 k2 v]
    )
  {"2018-05-22" {:A {123 "foo"}}})

Perfect, thank you!

I couldn't figure out how to compose MAP-VALS+ myself.