Spark extracting values from a Row

I have the following dataframe

val transactions_with_counts = sqlContext.sql(
  """SELECT user_id AS user_id, category_id AS category_id,
  COUNT(category_id) FROM transactions GROUP BY user_id, category_id""")

I'm trying to convert the rows to Rating objects but since x(0) returns an array this fails

val ratings = transactions_with_counts
  .map(x => Rating(x(0).toInt, x(1).toInt, x(2).toInt))

error: value toInt is not a member of Any

Solution 1:

Lets start with some dummy data:

val transactions = Seq((1, 2), (1, 4), (2, 3)).toDF("user_id", "category_id")

val transactions_with_counts = transactions
  .groupBy($"user_id", $"category_id")
  .count

transactions_with_counts.printSchema

// root
// |-- user_id: integer (nullable = false)
// |-- category_id: integer (nullable = false)
// |-- count: long (nullable = false)

There are a few ways to access Row values and keep expected types:

1. Pattern matching

   import org.apache.spark.sql.Row
   
   transactions_with_counts.map{
     case Row(user_id: Int, category_id: Int, rating: Long) =>
       Rating(user_id, category_id, rating)
   } 
   

2. Typed get* methods like getInt, getLong:

   transactions_with_counts.map(
     r => Rating(r.getInt(0), r.getInt(1), r.getLong(2))
   )
   

3. getAs method which can use both names and indices:

   transactions_with_counts.map(r => Rating(
     r.getAs[Int]("user_id"), r.getAs[Int]("category_id"), r.getAs[Long](2)
   ))
   

   It can be used to properly extract user defined types, including mllib.linalg.Vector. Obviously accessing by name requires a schema.

4. Converting to statically typed Dataset (Spark 1.6+ / 2.0+):

   transactions_with_counts.as[(Int, Int, Long)]
   

Solution 2:

Using Datasets you can define Ratings as follows:

case class Rating(user_id: Int, category_id:Int, count:Long)

The Rating class here has a column name 'count' instead of 'rating' as zero323 suggested. Thus the rating variable is assigned as follows:

val transactions_with_counts = transactions.groupBy($"user_id", $"category_id").count

val rating = transactions_with_counts.as[Rating]

This way you will not run into run-time errors in Spark because your Rating class column name is identical to the 'count' column name generated by Spark on run-time.