在 Apache-spark 中，如何添加稀疏向量？

Question

我正在尝试使用 spark 开发自己的前馈神经网络。但是我在 spark 的稀疏向量中找不到乘法、加法或除法等操作。该文件称它是使用微风矢量实现的。但我可以在微风中找到添加操作，但在火花矢量中找不到。如何解决这个问题？

Answer 1

Spark 的 Vector 实现不支持代数运算。不幸的是，Spark API 不再支持通过asBreeze 和fromBreeze 方法将SparkVectors 转换为BreezeVectors，因为相对于spark 包，这些方法已设为包私有。

但是，您可以编写自己的 Spark 到 Breeze 转换器。下面的代码使用类型类定义了这样一个转换器，它允许您始终获得最具体的类型。

import breeze.linalg.{Vector => BreezeVector, DenseVector => DenseBreezeVector, SparseVector => SparseBreezeVector}
import org.apache.spark.mllib.linalg.{Vector => SparkVector, DenseVector => DenseSparkVector, SparseVector => SparseSparkVector}

package object myPackage {

  implicit class RichSparkVector[I <: SparkVector](vector: I) {
    def asBreeze[O <: BreezeVector[Double]](implicit converter: Spark2BreezeConverter[I, O]): O = {
      converter.convert(vector)
    }
  }

  implicit class RichBreezeVector[I <: BreezeVector[Double]](breezeVector: I) {
    def fromBreeze[O <: SparkVector](implicit converter: Breeze2SparkConverter[I, O]): O = {
      converter.convert(breezeVector)
    }
  }
}

trait Spark2BreezeConverter[I <: SparkVector, O <: BreezeVector[Double]] {
  def convert(sparkVector: I): O
}

object Spark2BreezeConverter {
  implicit val denseSpark2DenseBreezeConverter = new Spark2BreezeConverter[DenseSparkVector, DenseBreezeVector[Double]] {
    override def convert(sparkVector: DenseSparkVector): DenseBreezeVector[Double] = {
      new DenseBreezeVector[Double](sparkVector.values)
    }
  }

  implicit val sparkSpark2SparseBreezeConverter = new Spark2BreezeConverter[SparseSparkVector, SparseBreezeVector[Double]] {
    override def convert(sparkVector: SparseSparkVector): SparseBreezeVector[Double] = {
      new SparseBreezeVector[Double](sparkVector.indices, sparkVector.values, sparkVector.size)
    }
  }

  implicit val defaultSpark2BreezeConverter = new Spark2BreezeConverter[SparkVector, BreezeVector[Double]] {
    override def convert(sparkVector: SparkVector): BreezeVector[Double] = {
      sparkVector match {
        case dv: DenseSparkVector => denseSpark2DenseBreezeConverter.convert(dv)
        case sv: SparseSparkVector => sparkSpark2SparseBreezeConverter.convert(sv)
      }
    }
  }
}

trait Breeze2SparkConverter[I <: BreezeVector[Double], O <: SparkVector] {
  def convert(breezeVector: I): O
}

object Breeze2SparkConverter {
  implicit val denseBreeze2DenseSparkVector = new Breeze2SparkConverter[DenseBreezeVector[Double], DenseSparkVector] {
    override def convert(breezeVector: DenseBreezeVector[Double]): DenseSparkVector = {
      new DenseSparkVector(breezeVector.data)
    }
  }

  implicit val sparseBreeze2SparseSparkVector = new Breeze2SparkConverter[SparseBreezeVector[Double], SparseSparkVector] {
    override def convert(breezeVector: SparseBreezeVector[Double]): SparseSparkVector = {
      val size = breezeVector.activeSize
      val indices = breezeVector.array.index.take(size)
      val data = breezeVector.data.take(size)
      new SparseSparkVector(size, indices, data)
    }
  }

  implicit val defaultBreeze2SparkVector = new Breeze2SparkConverter[BreezeVector[Double], SparkVector] {
    override def convert(breezeVector: BreezeVector[Double]): SparkVector = {
      breezeVector match {
        case dv: DenseBreezeVector[Double] => denseBreeze2DenseSparkVector.convert(dv)
        case sv: SparseBreezeVector[Double] => sparseBreeze2SparseSparkVector.convert(sv)
      }
    }
  }
}