Write a structured query that finds the first non-null value per group.
Protip™: Review the input arguments of the first standard function
Module: Spark SQL
Duration: 15 mins
val data = Seq(
(None, 0),
(None, 1),
(Some(2), 0),
(None, 1),
(Some(4), 1)).toDF("id", "group")
scala> data.show
+----+-----+
| id|group|
+----+-----+
|null| 0|
|null| 1|
| 2| 0|
|null| 1|
| 4| 1|
+----+-----+
+-----+--------------+
|group|first_non_null|
+-----+--------------+
| 1| 4|
| 0| 2|
+-----+--------------+