apache-spark - 替换深层嵌套模式 Spark Dataframe 中的值

Question

我是 pyspark 的新手。我试图了解如何访问具有多层嵌套结构和数组的 Parquet 文件。我需要用空值替换数据帧(带有嵌套模式)中的一些值，我见过这个 solution它适用于结构，但不确定它如何适用于数组。
我的架构是这样的

|-- unitOfMeasure: struct
|    |-- raw: struct
|    |    |-- id: string
|    |    |-- codingSystemId: string
|    |    |-- display: string
|    |-- standard: struct
|    |    |-- id: string
|    |    |-- codingSystemId: string
|-- Id: string
|-- actions: array
|    |-- element: struct
|    |    |-- action: string
|    |    |-- actionDate: string
|    |    |-- actor: struct
|    |    |    |-- actorId: string
|    |    |    |-- aliases: array
|    |    |    |    |-- element: struct
|    |    |    |    |    |-- value: string
|    |    |    |    |    |-- type: string
|    |    |    |    |    |-- assigningAuthority: string
|    |    |    |-- fullName: string

我想做的是替换unitOfMeasure.raw.id归零
和 actions.element.action与空
和 actions.element.actor.aliases.element.value使用 null 保持我的数据框的其余部分不变。
有什么办法可以实现这一目标吗？

Answer 1

对于数组列，与结构字段相比，它有点复杂。
一种选择是将数组分解为新列，以便您可以访问和更新嵌套结构。更新后，您必须重建初始数组列。

但我更喜欢使用高阶函数 transform 这是为 Spark >=2.4 引入的这里是一个例子:

输入DF:

 |-- actions: array (nullable = true)
 |    |-- element: struct (containsNull = true)
 |    |    |-- action: string (nullable = true)
 |    |    |-- actionDate: string (nullable = true)
 |    |    |-- actor: struct (nullable = true)
 |    |    |    |-- actorId: long (nullable = true)
 |    |    |    |-- aliases: array (nullable = true)
 |    |    |    |    |-- element: struct (containsNull = true)
 |    |    |    |    |    |-- assigningAuthority: string (nullable = true)
 |    |    |    |    |    |-- type: string (nullable = true)
 |    |    |    |    |    |-- value: string (nullable = true)
 |    |    |    |-- fullName: string (nullable = true)

+--------------------------------------------------------------+
|actions                                                       |
+--------------------------------------------------------------+
|[[action_name1, 2019-12-08, [2, [[aa, t1, v1]], full_name1]]] |
|[[action_name2, 2019-12-09, [3, [[aaa, t2, v2]], full_name2]]]|
+--------------------------------------------------------------+

我们将 lambda 函数传递给 transfrom选择所有结构字段并替换 actions.action和 actions.actor.aliases.value来自 null .

transform_expr = """transform (actions, x -> 
                               struct(null as action, 
                                      x.actionDate as actionDate, 
                                      struct(x.actor.actorId as actorId, 
                                             transform(x.actor.aliases, y -> 
                                                       struct(null as value, 
                                                              y.type as type, 
                                                              y.assigningAuthority as assigningAuthority)
                                                       ) as aliases,
                                            x.actor.fullName as fullName
                                      ) as actor
                                ))"""

df.withColumn("actions", expr(transform_expr)).show(truncate=False)

输出DF:

+------------------------------------------------+
|actions                                         |
+------------------------------------------------+
|[[, 2019-12-08, [2, [[, t1, aa]], full_name1]]] |
|[[, 2019-12-09, [3, [[, t2, aaa]], full_name2]]]|
+------------------------------------------------+