scala - Spark 中的并行 FP 增长

Question

我试图了解 FPTree 类的“添加”和“提取”方法：（https://github.com/apache/spark/blob/master/mllib/src/main/scala/org/apache/spark/ mllib/fpm/FPGrowth.scala）。

1. “摘要”变量的目的是什么？
2. 组列表在哪里？我假设它是以下内容，我是否正确：

val numParts = if (numPartitions > 0) numPartitions else data.partitions.length
val partitioner = new HashPartitioner(numParts)

3. 对于 {a,b,c} 、 {a,b} 、 {b,c} 的 3 个事务，所有频繁的“摘要”将包含什么？

def add(t: Iterable[T], count: Long = 1L): FPTree[T] = {
  require(count > 0)
  var curr = root
  curr.count += count
  t.foreach { item =>
    val summary = summaries.getOrElseUpdate(item, new Summary)
    summary.count += count
    val child = curr.children.getOrElseUpdate(item, {
      val newNode = new Node(curr)
      newNode.item = item
      summary.nodes += newNode
      newNode
    })
    child.count += count
    curr = child
  }
  this
}

def extract(
    minCount: Long,
    validateSuffix: T => Boolean = _ => true): Iterator[(List[T], Long)] = {
  summaries.iterator.flatMap { case (item, summary) =>
    if (validateSuffix(item) && summary.count >= minCount) {
      Iterator.single((item :: Nil, summary.count)) ++
        project(item).extract(minCount).map { case (t, c) =>
          (item :: t, c)
        }
    } else {
      Iterator.empty
    }
  }
}

Answer 1

经过一些实验，它非常简单：

1+2) 分区确实是集团代表。这也是条件交易的计算方式：

  private def genCondTransactions[Item: ClassTag](
      transaction: Array[Item],
      itemToRank: Map[Item, Int],
      partitioner: Partitioner): mutable.Map[Int, Array[Int]] = {
    val output = mutable.Map.empty[Int, Array[Int]]
    // Filter the basket by frequent items pattern and sort their ranks.
    val filtered = transaction.flatMap(itemToRank.get)
    ju.Arrays.sort(filtered)
    val n = filtered.length
    var i = n - 1
    while (i >= 0) {
      val item = filtered(i)
      val part = partitioner.getPartition(item)
      if (!output.contains(part)) {
        output(part) = filtered.slice(0, i + 1)
      }
      i -= 1
    }
    output
  }

3. 摘要只是保存事务中项目计数的助手。提取/项目将通过使用向上/向下递归和依赖的 FP-Trees（项目）生成 FIS，同时检查摘要是否需要遍历该路径。节点“a”的摘要将具有 {b:2,c:1}，节点“a”的子节点是“b”和“c”。