clojure prewalk with select-keys

Question

(clojure.walk/prewalk #(if (map? %)
                           (select-keys  % [:c])
                            %)
                      {:a 1 :b [{:c 3} {:d 4}] :c 5})
=>{:c 5}

why does this only find {:c 5} and not also {:c 3} ? I'm trying to write something that will pull out all key/value pairs that exist for any form and at any level for the key I specify.

Answer 1

When it your function is called with

{:c 5, :b [{:c 3} {:d 4}], :a 1}

...it returns:

{:c 5}

...thus discarding all other keys, including the :b branch, which is thus not traversed.