Gets the last record in the RelationalGroupedDataset.

The last API has several implementations as follows. The exact API used depends on the specific use case:

def last(columnName: String): Column
 Aggregate function: returns the last value of the column in a group.
def last(e: Column): Column
 Aggregate function: returns the last value in a group.
def last(columnName: String, ignoreNulls: Boolean): Column
 Aggregate function: returns the last value of the column in a group.
def last(e: Column, ignoreNulls: Boolean): Column
 Aggregate function: returns the last value in a group.

Let's look at example of invoking last on the DataFrame to output the last row:

import org.apache.spark.sql.functions._
 scala> statesPopulationDF.select(last("State")).show
 +------------------+
 |last(State, false)|
 +------------------+
 | Wyoming|
 +------------------+