On Sun, Dec 5, 2010 at 10:03 PM, Ken Wesson <kwess...@gmail.com> wrote:
> On Sun, Dec 5, 2010 at 9:12 PM, Alex Baranosky
> <alexander.barano...@gmail.com> wrote:
>> Hi guys,
>> I would like a function to be able to take an arbitrarily nested collection
>> and return a sequence of all values of a given key, such as :name, that
>> appears anywhere in the nested collection.
>> Does anything like this already exist?
>
> It does now:
>
> (defn values-of [k coll]
> (if-let [s (try (seq coll) (catch Exception _ nil))]
> (let [not-found (Object.)
> v (if (associative? coll) (get coll k not-found) not-found)
> v (if-not (= v not-found) [v])
> vs (map #(values-of k %) s)]
> (apply concat v vs))))
>
> user=> (values-of :k [1 2 {:k 3 :l 4} 5 #{6} [[{:k 2}] {:k {:a 3 :k 7}}]])
> (3
> 2
> {:a 3, :k 7}
> 7)
>
> It won't quite work perfectly for java.util collections, specifically
> because (associative? (java.util.HashMap.)) comes back false for some
> reason.
This should work even for Java collections including maps:
(defn values-of [k coll]
(if (instance? java.util.Map$Entry coll)
(recur k [(key coll) (val coll)])
(if-let [s (try (seq coll) (catch Exception _ nil))]
(let [not-found (Object.)
v (if (or (associative? coll) (instance? java.util.Map coll))
(get coll k not-found) not-found)
v (if-not (= v not-found) [v])
vs (map #(values-of k %) s)]
(apply concat v vs)))))
user=> (values-of :k (doto (java.util.HashMap.) (.put :k "foo")))
("foo")
user=> (values-of :k (doto (java.util.HashMap.) (.put {:k 3} "foo")))
(3)
The new if at the start is because Clojure doesn't treat non-Clojure
Map$Entries as equivalent to [key val] so I turn all Map$Entries into
such vectors manually.
As you can see, it will delve into both the keys and the values of
even java.util Maps now.
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