Add ValueIncrementableHashMapAccumulator

core/src/main/scala/org/apache/spark/util/collection/ValueIncrementableHashMapAccumulator.scala

@@ -0,0 +1,35 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.spark.util.collection
+
+import scala.collection.mutable.HashMap
+
+class ValueIncrementableHashMapAccumulator[T] extends HashMap[T,Long] with Serializable {
+
+  override def += (kv : (T, Long)): this.type = {
+    if(this.contains(kv._1)){
+      // Key already exists, just increment the value for that Key
+      this.put(kv._1, kv._2 + this.get(kv._1).get)
+    }
+    else{
+        this.put(kv._1, kv._2)
+    }
+    this
+  }
+
+}