How do I groupby and concat a list in a Dataframe Spark Scala

Question

I have a dataframe with two columns with data as below

+----+-----------------+
|acct|           device|
+----+-----------------+
|   B|       List(3, 4)|
|   C|       List(3, 5)|
|   A|       List(2, 6)|
|   B|List(3, 11, 4, 9)|
|   C|       List(5, 6)|
|   A|List(2, 10, 7, 6)|
+----+-----------------+

And I need the result as below

+----+-----------------+
|acct|           device|
+----+-----------------+
|   B|List(3, 4, 11, 9)|
|   C|    List(3, 5, 6)|
|   A|List(2, 6, 7, 10)|
+----+-----------------+

I tried as below but ,it seems to be not working

df.groupBy("acct").agg(concat("device"))

df.groupBy("acct").agg(collect_set("device"))

Please let me know how can I achieve this using Scala?

Answer 1

You can start by exploding the device column and continue as you did - but note that it might not preserve the order of the lists (which anyway isn't guaranteed in any group by):

val result = df.withColumn("device", explode($"device"))
  .groupBy("acct")
  .agg(collect_set("device"))

result.show(truncate = false)
// +----+-------------------+
// |acct|collect_set(device)|
// +----+-------------------+
// |B   |[9, 3, 4, 11]      |
// |C   |[5, 6, 3]          |
// |A   |[2, 6, 10, 7]      |
// +----+-------------------+