Partial fix to techascent/tech.ml.dataset#155

java/tech/v3/datatype/Buffer.java

@@ -46,8 +46,9 @@ public interface Buffer extends DatatypeBase, Iterable, IFn,
   default int size() { return RT.intCast(lsize()); }
   default Object get(int idx) { return readObject(idx); }
   default Object set(int idx, Object val) {
+    Object current = get(idx);
     writeObject(idx, val);
-    return null;
+    return current;
   }
   default boolean isEmpty() { return lsize() == 0; }
   default Object[] toArray() {

src/tech/v3/datatype/argops.clj

@@ -32,7 +32,7 @@
             Buffer
             UnaryOperator BinaryOperator
             UnaryPredicate BinaryPredicate]
-           [java.util Comparator Arrays List Map Iterator]
+           [java.util Comparator Arrays List Map Iterator Collections Random]
            [org.roaringbitmap RoaringBitmap]))
 
 
@@ -504,3 +504,24 @@
                            (->binary-predicate partition-pred)))))
   (^Iterable [unary-op item-iterable]
    (argpartition-by unary-op :tech.numerics/eq item-iterable)))
+
+
+(defn argshuffle
+  "Serially shuffle N indexes into a an array of data.
+  Returns an array of indexes."
+  ([^long n-indexes {:keys [seed container-type]
+                     :or {container-type :jvm-heap}}]
+   (let [data (if (< n-indexes (long Integer/MAX_VALUE))
+                (dtype-cmc/make-container container-type :int32 (range n-indexes))
+                (dtype-cmc/make-container container-type :int64 (range n-indexes)))
+         ^Random rgen (when seed
+                        (if (number? seed)
+                          (java.util.Random. (int seed))
+                          seed))
+         data-buf (dtype-base/->buffer data)]
+     (if rgen
+       (Collections/shuffle data-buf rgen)
+       (Collections/shuffle data-buf))
+     data))
+  ([n-indexes]
+   (argshuffle n-indexes nil)))

test/tech/v3/datatype_test.clj

@@ -557,6 +557,15 @@
           {:keys [result missing]} (dfn/fill-range long-test-data 3)])))
 
 
+(deftest argshuffle-test
+  (let [test-data (dtype/make-container :float32 (range 20))
+        buf (dtype/->buffer test-data)]
+    (is (= (vec (argops/argshuffle 20 {:seed 20}))
+           (vec (argops/argshuffle 20 {:seed 20}))))
+    (is (not= (vec (argops/argshuffle 20))
+              (vec (argops/argshuffle 20))))))
+
+
 (deftest ctime-min-max
   (is (dtype-proto/has-constant-time-min-max? 4))
   (is (= 4 (dtype-proto/constant-time-min 4)))