Is there an explode function equivalent in plain Scala? - scala

Question

I am trying to look for explode function or its equivalent in plain scala rather Spark.
Using the explode function in Spark, I was able to flatten a row with multiple elements into multiple rows as below.
scala> import org.apache.spark.sql.functions.explode
import org.apache.spark.sql.functions.explode
scala> val test = spark.read.json(spark.sparkContext.parallelize(Seq("""{"a":1,"b":[2,3]}""")))
scala> test.schema
res1: org.apache.spark.sql.types.StructType = StructType(StructField(a,LongType,true), StructField(b,ArrayType(LongType,true),true))
scala> test.show
+---+------+
| a| b|
+---+------+
| 1|[2, 3]|
+---+------+
scala> val flat = test.withColumn("b",explode($"b"))
flat: org.apache.spark.sql.DataFrame = [a: bigint, b: bigint]
scala> flat.show
+---+---+
| a| b|
+---+---+
| 1| 2|
| 1| 3|
+---+---+
Is there an explode equivalent function in plain scala without using Spark ? Is there anyway I can implement it if there is no explode function available in scala ?

Answer 1

Simple flatMap should help you in this case. I don't know exact data structure, which you would like to work with in scala, but let's take a bit artificial example:
val l: List[(Int, List[Int])] = List(1 -> List(2, 3))
val result: List[(Int, Int)] = l.flatMap {
case (a, b) => b.map(i => a -> i)
}
println(result)
Which will produce next result:
List((1,2), (1,3))
UPDATE
As suggested in comment section by #jwvh, or same result may be achieved using for-comprehension construction and hiding explicit flatMap & map invocations:
val result2: List[(Int, Int)] = for((a, bList) <- l; b <- bList) yield a -> b
Hope this helps!