如何设置一个空结构，所有字段为空，在火花中为空答案

【问题标题】：How to set an empty struct with all fields null, null in spark如何设置一个空结构，所有字段为空，在火花中为空
【发布时间】：2022-01-18 02:39:11
【问题描述】：

我有这个数据框：

+----+--------------------------------+
|name|dates                           |
+----+--------------------------------+
|A   |[[1994, 12, 11], [,,]]          |
|B   |[[1994, 12, 11], [1994, 12, 15]]|
+----+--------------------------------+

使用此架构：

root
 |-- name: string (nullable = true)
 |-- dates: struct (nullable = true)
 |    |-- start_date: struct (nullable = true)
 |    |    |-- year: integer (nullable = true)
 |    |    |-- month: integer (nullable = true)
 |    |    |-- day: integer (nullable = true)
 |    |-- end_date: struct (nullable = true)
 |    |    |-- year: integer (nullable = true)
 |    |    |-- month: integer (nullable = true)
 |    |    |-- day: integer (nullable = true)

我想把它作为输出当end_date内的所有字段为null时，设置结束日期为null

+----+--------------------------------+
|name|dates                           |
+----+--------------------------------+
|A   |[[1994, 12, 11],]               |
|B   |[[1994, 12, 11], [1994, 12, 15]]|
+----+--------------------------------+

【问题讨论】：

标签： scala apache-spark apache-spark-sql

【解决方案1】：

您可以通过从现有属性重新创建新结构来更新结构列dates，并使用when 表达式检查所有end_dates 属性是否为空：

val df2 = df.withColumn(
  "dates",
  struct(
    col("dates.start_date"), // keep start_date
    when(
      Seq("year", "month", "day")
        .map(x => col(s"dates.end_date.$x").isNull)
        .reduce(_ and _),
      lit(null).cast("struct<year:int,month:int,day:int>")
    ).otherwise(col("dates.end_date")).alias("end_date") // set end_date to null if all attr are null
  )
)

df2.show(false)
//+----+--------------------------------+
//|name|dates                           |
//+----+--------------------------------+
//|A   |[[1994, 12, 11],]               |
//|B   |[[1994, 12, 11], [1994, 12, 25]]|
//+----+--------------------------------+

【讨论】：