How to calculate the mean of a dataframe column and find the top 10%

Question

I am very new to Scala and Spark, and am working on some self-made exercises using baseball statistics. I am using a case class create a RDD and assign a schema to the data, and am then turning it into a DataFrame so I can use SparkSQL to select groups of players via their stats that meet certain criteria.

Once I have the subset of players I am interested in looking at further, I would like to find the mean of a column; eg Batting Average or RBIs. From there I would like to break all the players into percentile groups based on their average performance compared to all players; the top 10%, bottom 10%, 40-50%

I've been able to use the DataFrame.describe() function to return a summary of a desired column (mean, stddev, count, min, and max) all as strings though. Is there a better way to get just the mean and stddev as Doubles, and what is the best way of breaking the players into groups of 10-percentiles?

So far my thoughts are to find the values that bookend the percentile ranges and writing a function that groups players via comparators, but that feels like it is bordering on reinventing the wheel.

I have the following imports currently:

 import org.apache.spark.rdd.RDD 
 import org.apache.spark.sql.SQLContext 
 import org.apache.spark.{SparkConf, SparkContext} 
 import org.joda.time.format.DateTimeFormat  

Answer 1

This is the import you need, and how to get the mean for a column named "RBIs":

import org.apache.spark.sql.functions._
df.select(avg($"RBIs")).show()

For the standard deviation, see scala - Calculate the standard deviation of grouped data in a Spark DataFrame - Stack Overflow

For grouping by percentiles, I suggest defining a new column via a user-defined function (UDF), and using groupBy on that column. See

• Spark SQL and DataFrames - Spark 1.5.1 Documentation - udf registration

Answer 2

This is also returns average of column

df.select(mean(df("ColumnName"))).show()
+----------------+
| avg(ColumnName)|
+----------------+
|230.522453845909|
+----------------+