add value extraction param to distinct

[rod naph]

(Please correct me if there's a better way to do this)

distinct currently only takes one argument, the sequence to filter.  if you're filtering a single level seq that's fine, but if you can't filter any more interesting elements, for example...

[{:id 1 :value "foo"} {:id 2 :value "foo"} {:id 3 :value "bar"}]

i suggest adding a first parameter to extract the value from each element being compared.

(defn distinct

  "Returns a lazy sequence of the elements identified by f of coll with duplicates removed"

  {:added "1.0"

   :static true}

  ([coll] (distinct identity coll))

  ([f coll]

    (let [step (fn step [xs seen]

                   (lazy-seq

                    ((fn [[vs :as xs] seen]

                      (let [v (f vs)]

                        (when-let [s (seq xs)]

                          (if (contains? seen v)

                            (recur (rest s) seen)

                            (cons vs (step (rest s) (conj seen v)))))))

                     xs seen)))]

      (step coll #{}))))

Then allowing to use like...

(->> values

     (distinct :value)

     (map etc...))

Or is there a better way of doing this in core?

[Tom Jack]

Relevant old discussion: https://groups.google.com/d/msg/clojure/wB2tin3GTh8/ZZKIpKyQaeQJ

--
You received this message because you are subscribed to the Google Groups "Clojure Dev" group.
To unsubscribe from this group and stop receiving emails from it, send an email to clojure-dev...@googlegroups.com.
To post to this group, send email to cloju...@googlegroups.com.
Visit this group at http://groups.google.com/group/clojure-dev.
For more options, visit https://groups.google.com/groups/opt_out.