使用 GroupBy Pivot Agg 在 Scala Spark 中重塑 DataFrame

Question

我有一个数据框：

+---+---+----+  
| id|key|name|  
+---+---+----+  
| 10|  1|   a|  
| 11|  1|   b|  
| 12|  1|   c|  
| 20|  2|   d|  
| 21|  2|   e|  
| 30|  3|   f|  
| 31|  3|   g|  
| 32|  3|   h|  
| 33|  3|   i|  
| 40|  4|   j|  
| 41|  4|   k|  
| 42|  4|   l|  
| 43|  4|   m|  
| 44|  4|   n|  
+---+---+----+  

val DF = Seq((10, 1, "a"), (11, 1, "b"), (12, 1, "c"), (20, 2, "d"), (21, 2,"e"), (30, 3, "f"), (31, 3, "g"), (32, 3, "h"), (33, 3, "i"), (40, 4, "j"), (41, 4, "k"), (42, 4, "l"), (43, 4, "m"), (44, 4, "n")).toDF("id", "key", "name")

我正在尝试获得以下输出（在按键聚合时将行值重新整形为列值时，名称和 ID 限制为 4 列）：

要求的输出：

|key|name_1|id_1|name_2|id_2|name_3|id_3|name_4|id_4|  
|  1|     a|  10|     b|  11|     c|  12|  null|null|  
|  2|     d|  20|     e|  21|  null|null|  null|null|  
|  3|     f|  30|     g|  31|     h|  32|     i|  33|  
|  4|     j|  40|     k|  41|     l|  42|     m|  43|  

我是 Scala-Spark 的初学者。 欢迎任何帮助/建议/问题。

Answer 1

使用键聚合行（groupBy）并将 id 和 name 收集到一个列表中。将键收集到列表中后，您应该能够在 select 语句中引用它们。

 import org.apache.spark.sql.functions.collect_list

 df.groupBy(df("key"))
      .agg(collect_list(df("name")).alias("name_list"),
           collect_list("id").alias("id_list"))
      .selectExpr(
        "key",
        "name_list[0] as name_1",
        "id_list[0] as id_1",
        "name_list[1] as name_2",
        "id_list[1] as id_2",
        "name_list[2] as name_3",
        "id_list[2] as id_3",
        "name_list[3] as name_4",
        "id_list[3] as id_4"
      ).show



+---+------+----+------+----+------+----+------+----+
|key|name_1|id_1|name_2|id_2|name_3|id_3|name_4|id_4|
+---+------+----+------+----+------+----+------+----+
|  1|     a|  10|     b|  11|     c|  12|  null|null|
|  3|     f|  30|     g|  31|     h|  32|     i|  33|
|  4|     j|  40|     k|  41|     l|  42|     m|  43|
|  2|     d|  20|     e|  21|  null|null|  null|null|
+---+------+----+------+----+------+----+------+----+