scala> val accum = sc.accumulator(0, "My Accumulator")

accum: spark.Accumulator[Int] = 0

scala> sc.parallelize(Array(1, 2, 3, 4)).foreach(x => accum += x)

...

10/09/29 18:41:08 INFO SparkContext: Tasks finished in 0.317106 s

scala> accum.value

res2: Int = 10

object VectorAccumulatorParam extends AccumulatorParam[Vector] {

  def zero(initialValue: Vector): Vector = {

    Vector.zeros(initialValue.size)

  }

  def addInPlace(v1: Vector, v2: Vector): Vector = {

    v1 += v2

  }

}

// Then, create an Accumulator of this type:

val vecAccum = sc.accumulator(new Vector(...))(VectorAccumulatorParam)