scala - 如何在groupBy之后将值聚合到集合中？

Question

我有一个具有如下架构的数据框:

[visitorId: string, trackingIds: array<string>, emailIds: array<string>]

正在寻找一种方法按 guestid 对此数据框进行分组(或者可能汇总？)，其中 TrackingIds 和 emailIds 列将附加在一起。例如，如果我的初始 df 看起来像:

visitorId   |trackingIds|emailIds
+-----------+------------+--------
|a158|      [666b]      |    [12]
|7g21|      [c0b5]      |    [45]
|7g21|      [c0b4]      |    [87]
|a158|      [666b, 777c]|    []

我希望我的输出 df 看起来像这样

visitorId   |trackingIds|emailIds
+-----------+------------+--------
|a158|      [666b,666b,777c]|      [12,'']
|7g21|      [c0b5,c0b4]     |      [45, 87]

尝试使用groupBy和agg运算符，但运气不佳。

Answer 1

Spark >= 2.4

您可以用内置 flatten function 替换 flatten udf

import org.apache.spark.sql.functions.flatten

其余部分保持原样。

Spark >= 2.0，< 2.4

这是可能的，但相当昂贵。使用您提供的数据:

case class Record(
    visitorId: String, trackingIds: Array[String], emailIds: Array[String])

val df = Seq(
  Record("a158", Array("666b"), Array("12")),
  Record("7g21", Array("c0b5"), Array("45")),
  Record("7g21", Array("c0b4"), Array("87")),
  Record("a158", Array("666b",  "777c"), Array.empty[String])).toDF

和一个辅助函数:

import org.apache.spark.sql.functions.udf

val flatten = udf((xs: Seq[Seq[String]]) => xs.flatten)

我们可以用占位符填充空白:

import org.apache.spark.sql.functions.{array, lit, when}

val dfWithPlaceholders = df.withColumn(
  "emailIds", 
  when(size($"emailIds") === 0, array(lit(""))).otherwise($"emailIds"))

collect_lists 和 展平:

import org.apache.spark.sql.functions.{array, collect_list}

val emailIds = flatten(collect_list($"emailIds")).alias("emailIds")
val trackingIds = flatten(collect_list($"trackingIds")).alias("trackingIds")

df
  .groupBy($"visitorId")
  .agg(trackingIds, emailIds)

// +---------+------------------+--------+
// |visitorId|       trackingIds|emailIds|
// +---------+------------------+--------+
// |     a158|[666b, 666b, 777c]|  [12, ]|
// |     7g21|      [c0b5, c0b4]|[45, 87]|
// +---------+------------------+--------+

使用静态类型的数据集:

df.as[Record]
  .groupByKey(_.visitorId)
  .mapGroups { case (key, vs) => 
    vs.map(v => (v.trackingIds, v.emailIds)).toArray.unzip match {
      case (trackingIds, emailIds) => 
        Record(key, trackingIds.flatten, emailIds.flatten)
  }}

// +---------+------------------+--------+
// |visitorId|       trackingIds|emailIds|
// +---------+------------------+--------+
// |     a158|[666b, 666b, 777c]|  [12, ]|
// |     7g21|      [c0b5, c0b4]|[45, 87]|
// +---------+------------------+--------+

Spark 1.x

可以转换为RDD和分组

import org.apache.spark.sql.Row

dfWithPlaceholders.rdd
  .map {
     case Row(id: String, 
       trcks: Seq[String @ unchecked],
       emails: Seq[String @ unchecked]) => (id, (trcks, emails))
  }
  .groupByKey
  .map {case (key, vs) => vs.toArray.unzip match {
    case (trackingIds, emailIds) => 
      Record(key, trackingIds.flatten, emailIds.flatten)
  }}
  .toDF

// +---------+------------------+--------+
// |visitorId|       trackingIds|emailIds|
// +---------+------------------+--------+
// |     7g21|      [c0b5, c0b4]|[45, 87]|
// |     a158|[666b, 666b, 777c]|  [12, ]|
// +---------+------------------+--------+