提取列值并将其作为Spark数据帧中的数组分配给另一列 [英] Extract a column value and assign it to another column as an array in Spark dataframe

问题描述

我有一个带有以下各列的Spark数据框.

I have a Spark Dataframe with the below columns.

C1 | C2 | C3| C4
1  | 2  | 3 | S1
2  | 3  | 3 | S2
4  | 5  | 3 | S2

我想通过从C4列中获取不同的值来生成另一个C5列就像C5

I want to generate another column C5 by taking distinct values from column C4 like C5

[S1,S2]
[S1,S2]
[S1,S2]

有人可以帮助我如何使用Scala在Spark数据框中实现这一目标吗?

Can somebody help me how to achieve this in Spark data frame using Scala?

推荐答案

您可能希望收集第4列中的不同项目，然后将它们放在列表"中，然后使用 withColumn 创建一个通过创建始终返回常量列表的 udf 来创建新列 C5 :

You might want to collect the distinct items from column 4 and put them in a List firstly, and then use withColumn to create a new column C5 by creating a udf that always return a constant list:

val uniqueVal = df.select("C4").distinct().map(x => x.getAs[String](0)).collect.toList    
def myfun: String => List[String] = _ => uniqueVal 
def myfun_udf = udf(myfun)

df.withColumn("C5", myfun_udf(col("C4"))).show

+---+---+---+---+--------+
| C1| C2| C3| C4|      C5|
+---+---+---+---+--------+
|  1|  2|  3| S1|[S2, S1]|
|  2|  3|  3| S2|[S2, S1]|
|  4|  5|  3| S2|[S2, S1]|
+---+---+---+---+--------+

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