Faster non-caching iteration of the ds columns.

Author: cnuernber

deps.edn

@@ -14,7 +14,7 @@
    :exec-fn codox.main/-main
    :exec-args {:group-id "techascent"
                :artifact-id "tech.ml.dataset"
-               :version "7.049"
+               :version "7.050-SNAPSHOT"
                :name "TMD"
                :description "A Clojure high performance data processing system"
                :metadata {:doc/format :markdown}

src/tech/v3/libs/arrow.clj

@@ -1173,7 +1173,7 @@ Dependent block frames are not supported!!")
                             (dtype/set-constant! -1))
                           (dtype/->byte-array))
         nodes-buffs-lens
-        (->> (ds-base/columns dataset)
+        (->> (.values ^Map dataset)
              (hamf/pmap (fn [col]
                           (let [col-missing (ds-proto/missing col)
                                 n-missing (dtype/ecount col-missing)