Convert null values to empty array in Spark DataFrame

Question

I have a Spark data frame where one column is an array of integers. The column is nullable because it is coming from a left outer join. I want to convert all null values to

Answer 1

With a slight modification to zero323's approach, I was able to do this without using a udf in Spark 2.3.1.

val df = Seq("a" -> Array(1,2,3), "b" -> null, "c" -> Array(7,8,9)).toDF("id","numbers")
df.show
+---+---------+
| id|  numbers|
+---+---------+
|  a|[1, 2, 3]|
|  b|     null|
|  c|[7, 8, 9]|
+---+---------+

val df2 = df.withColumn("numbers", coalesce($"numbers", array()))
df2.show
+---+---------+
| id|  numbers|
+---+---------+
|  a|[1, 2, 3]|
|  b|       []|
|  c|[7, 8, 9]|
+---+---------+