CODEWITHSUNDEEP
scalaapache-sparkapache-spark-sqldistributed-computingdatabricks
Feynman27
Feynman27

Reputation: 3267

Exploding nested Struct in Spark dataframe

I'm working through a Databricks example. The schema for the dataframe looks like:

> parquetDF.printSchema
root
|-- department: struct (nullable = true)
|    |-- id: string (nullable = true)
|    |-- name: string (nullable = true)
|-- employees: array (nullable = true)
|    |-- element: struct (containsNull = true)
|    |    |-- firstName: string (nullable = true)
|    |    |-- lastName: string (nullable = true)
|    |    |-- email: string (nullable = true)
|    |    |-- salary: integer (nullable = true)

In the example, they show how to explode the employees column into 4 additional columns:

val explodeDF = parquetDF.explode($"employees") { 
case Row(employee: Seq[Row]) => employee.map{ employee =>
  val firstName = employee(0).asInstanceOf[String]
  val lastName = employee(1).asInstanceOf[String]
  val email = employee(2).asInstanceOf[String]
  val salary = employee(3).asInstanceOf[Int]
  Employee(firstName, lastName, email, salary)
 }
}.cache()
display(explodeDF)

How would I do something similar with the department column (i.e. add two additional columns to the dataframe called "id" and "name")? The methods aren't exactly the same, and I can only figure out how to create a brand new data frame using:

val explodeDF = parquetDF.select("department.id","department.name")
display(explodeDF)

If I try:

val explodeDF = parquetDF.explode($"department") { 
  case Row(dept: Seq[String]) => dept.map{dept => 
  val id = dept(0) 
  val name = dept(1)
  } 
}.cache()
display(explodeDF)

I get the warning and error:

<console>:38: warning: non-variable type argument String in type pattern Seq[String] is unchecked since it is eliminated by erasure
            case Row(dept: Seq[String]) => dept.map{dept => 
                           ^
<console>:37: error: inferred type arguments [Unit] do not conform to    method explode's type parameter bounds [A <: Product]
  val explodeDF = parquetDF.explode($"department") { 
                                   ^

Upvotes: 35

Views: 91504

Answers (3)

DHARIN PAREKH
DHARIN PAREKH

Reputation: 630

In my opinion the most elegant solution is to star expand a Struct using a select operator as shown below:

var explodedDf2 = explodedDf.select("department.*","*")

https://docs.databricks.com/spark/latest/spark-sql/complex-types.html

Upvotes: 52

gsamaras
gsamaras

Reputation: 73366

You could use something like that:

var explodeDF = explodeDF.withColumn("id", explodeDF("department.id"))
explodeDeptDF = explodeDeptDF.withColumn("name", explodeDeptDF("department.name"))

which you helped me into and these questions:

Upvotes: 25

Feynman27
Feynman27

Reputation: 3267

This seems to work (though maybe not the most elegant solution). 

var explodeDF2 = explodeDF.withColumn("id", explodeDF("department.id"))
explodeDF2 = explodeDF2.withColumn("name", explodeDF2("department.name"))

Upvotes: 3

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