Use query metadata rather than Field metadata

src/metabase/feature_extraction/core.clj

@@ -67,11 +67,11 @@
 
 (defmethod extract-features (type Field)
   [opts field]
-  (let [dataset (values/field-values field (extract-query-opts opts))]
-    {:features (->> dataset
+  (let [{:keys [field row]} (values/field-values field (extract-query-opts opts))]
+    {:features (->> row
                     (field->features opts field)
                     (merge {:table (Table (:table_id field))}))
-     :sample?  (sampled? opts dataset)}))
+     :sample?  (sampled? opts row)}))
 
 (defmethod extract-features (type Table)
   [opts table]

src/metabase/feature_extraction/feature_extractors.clj

@@ -503,9 +503,7 @@
                               (#{:day :month :year :quarter :week} unit))
                   {:histogram-hour (redux/pre-step
                                     h/histogram-categorical
-                                    ;; TOFIX: this is an ugly workaround
-                                    #(when (and % (not (instance? java.sql.Date %)))
-                                       (.getHours ^java.util.Date %)))})))
+                                    (somef (memfn ^java.util.Date getHours)))})))
    (merge-juxt
     histogram-extractor
     (field-metadata-extractor field)

src/metabase/feature_extraction/values.clj

@@ -7,16 +7,16 @@
 (defn field-values
   "Return all the values of FIELD for QUERY."
   [{:keys [id table_id] :as field} query]
-  (->> (qp/process-query
-         {:type       :query
-          :database   (metadata/db-id field)
-          :query      (-> query
-                          (ql/source-table table_id)
-                          (ql/fields id))
-          :middleware {:format-rows? false}})
-       :data
-       :rows
-       (map first)))
+  (let [{:keys [rows cols]} (->> (qp/process-query
+                                   {:type       :query
+                                    :database   (metadata/db-id field)
+                                    :query      (-> query
+                                                    (ql/source-table table_id)
+                                                    (ql/fields id))
+                                    :middleware {:format-rows? false}})
+                                 :data)]
+    {:row   (map first rows)
+     :field (first cols)}))
 
 (defn query-values
   "Return all values for QUERY."