我试图理解fptree类的“add”和“extract”方法：(https://github.com/apache/spark/blob/master/mllib/src/main/scala/org/apache/spark/mllib/fpm/fpgrowth.scala).
“summaries”变量的用途是什么？
小组名单在哪里？我假设是这样的，对吗

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

对于{a，b，c}，{a，b}，{b，c}这三个经常发生的事务，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
    }
  }
}