Sort by a key, but value has more than one element using Scala - arrays

Question

I'm very new to Scala on Spark and wondering how you might create key value pairs, with the key having more than one element. For example, I have this dataset for baby names:
Year, Name, County, Number
2000, JOHN, KINGS, 50
2000, BOB, KINGS, 40
2000, MARY, NASSAU, 60
2001, JOHN, KINGS, 14
2001, JANE, KINGS, 30
2001, BOB, NASSAU, 45
And I want to find the most frequently occurring for each county, regardless of the year. How might I go about doing that?
I did accomplish this using a loop. Refer to below. But I'm wondering if there is shorter way to do this that utilizes Spark and Scala duality. (i.e. can I decrease computation time?)
val names = sc.textFile("names.csv").map(l => l.split(","))
val uniqueCounty = names.map(x => x(2)).distinct.collect
for (i <- 0 to uniqueCounty.length-1) {
val county = uniqueCounty(i).toString;
val eachCounty = names.filter(x => x(2) == county).map(l => (l(1),l(4))).reduceByKey((a,b) => a + b).sortBy(-_._2);
println("County:" + county + eachCounty.first)
}

Answer 1

Here is the solution using RDD. I am assuming you need top occurring name per county.
val data = Array((2000, "JOHN", "KINGS", 50),(2000, "BOB", "KINGS", 40),(2000, "MARY", "NASSAU", 60),(2001, "JOHN", "KINGS", 14),(2001, "JANE", "KINGS", 30),(2001, "BOB", "NASSAU", 45))
val rdd = sc.parallelize(data)
//Reduce the uniq values for county/name as combo key
val uniqNamePerCountyRdd = rdd.map(x => ((x._3,x._2),x._4)).reduceByKey(_+_)
// Group names per county.
val countyNameRdd = uniqNamePerCountyRdd.map(x=>(x._1._1,(x._1._2,x._2))).groupByKey()
// Sort and take the top name alone per county
countyNameRdd.mapValues(x => x.toList.sortBy(_._2).take(1)).collect
Output:
res8: Array[(String, List[(String, Int)])] = Array((KINGS,List((JANE,30))), (NASSAU,List((BOB,45))))

Answer 2

You could use the spark-csv and the Dataframe API. If you are using the new version of Spark (2.0) it is slightly different. Spark 2.0 has a native csv data source based on spark-csv.
Use spark-csv to load your csv file into a Dataframe.
val df = sqlContext.read.format("com.databricks.spark.csv")
.option("header", "true")
.option("inferSchema", "true")
.load(new File(getClass.getResource("/names.csv").getFile).getAbsolutePath)
df.show
Gives output:
+----+----+------+------+
|Year|Name|County|Number|
+----+----+------+------+
|2000|JOHN| KINGS| 50|
|2000| BOB| KINGS| 40|
|2000|MARY|NASSAU| 60|
|2001|JOHN| KINGS| 14|
|2001|JANE| KINGS| 30|
|2001| BOB|NASSAU| 45|
+----+----+------+------+
DataFrames uses a set of operations for structured data manipulation. You could use some basic operations to become your result.
import org.apache.spark.sql.functions._
df.select("County","Number").groupBy("County").agg(max("Number")).show
Gives output:
+------+-----------+
|County|max(Number)|
+------+-----------+
|NASSAU| 60|
| KINGS| 50|
+------+-----------+
Is this what you are trying to achieve?
Notice the import org.apache.spark.sql.functions._ which is needed for the agg() function.
More information about Dataframes API
EDIT
For correct output:
df.registerTempTable("names")
//there is probably a better query for this
sqlContext.sql("SELECT * FROM (SELECT Name, County,count(1) as Occurrence FROM names GROUP BY Name, County ORDER BY " +
"count(1) DESC) n").groupBy("County", "Name").max("Occurrence").limit(2).show
Gives output:
+------+----+---------------+
|County|Name|max(Occurrence)|
+------+----+---------------+
| KINGS|JOHN| 2|
|NASSAU|MARY| 1|
+------+----+---------------+