[reductions] New maximum reducer

Author: harold

src/tech/v3/dataset/reductions.clj

@@ -134,6 +134,19 @@ user> (ds-reduce/group-by-column-agg
     hamf-proto/Finalize
     (finalize [this v] (deref v))))
 
+(defn maximum-rf
+  ([]
+   Double/NaN)
+  ([eax v]
+   (if (Double/isNaN eax)
+     v
+     (max (double v) (double eax))))
+  ([eax]
+   eax))
+
+(defn maximum
+  [colname]
+  (reducer->column-reducer maximum-rf colname))
 
 (deftype BitmapConsumer [^RoaringBitmap bitmap]
   LongConsumer
@@ -494,7 +507,7 @@ _unnamed [4 5]:
                        k v
                        (let [vv (finalize-fn v)]
                          (.lock ll)
-                         (try 
+                         (try
                            (.accept ^Consumer c vv)
                            (finally
                              (.unlock ll))))))

test/tech/v3/dataset/reductions_test.clj

@@ -370,6 +370,14 @@
 
     ))
 
+(deftest maximum-test
+  (let [ds (ds/->dataset {:x (repeatedly 100 rand)})
+        ev (last (:x (ds/sort-by-column ds :x)))
+        out-ds (ds-reduce/aggregate {:max-x (ds-reduce/maximum :x)} ds)]
+    (is (= 1 (ds/row-count out-ds)))
+    (is (= (first (:max-x out-ds))
+           ev))))
+
 (comment
 
   (do
@@ -435,7 +443,7 @@
 
 
   (dotimes [idx 100]
-    (time 
+    (time
      (ds-reduce/group-by-column-agg
       :a
       (into {} (for [col (-> one-hot :one-hot-table vals)