anish749 · January 25, 2026 04:00 · Chandraprabu · Oct 23, 2022 · kennyishihara · Feb 3, 2023
diff --git a/MostCommonValue.scala b/MostCommonValue.scala
 package org.anish.spark.mostcommonvalue

 import org.apache.spark.sql.Row
 import org.apache.spark.sql.expressions.{MutableAggregationBuffer, UserDefinedAggregateFunction}
 import org.apache.spark.sql.types._

 import scalaz.Scalaz._

 /**
  * Spark User Defined Aggregate Function to calculate the most frequent value in a column. This is similar to
  * Statistical Mode. When there are two random values, this function selects any one. When calculating mode, both
  * these values together is considered as mode.
  *
  * Usage:
  *
  * DataFrame / DataSet DSL
  * val mostCommonValue = new MostCommonValue
  * df.groupBy("group_id").agg(mostCommonValue(col("mode_column")), mostCommonValue(col("city")))
  *
  * Spark SQL:
  * sqlContext.udf.register("mode", new MostCommonValue)
  * %sql
  * -- Use a group_by statement and call the UDAF.
  * select group_id, mode(id) from table group by group_id
  * 
  * Reference: https://docs.databricks.com/spark/latest/spark-sql/udaf-scala.html
  *
  * Created by anish on 26/05/17.
  */
 class MostCommonValue extends UserDefinedAggregateFunction {

  // This is the input fields for your aggregate function.
  // We use StringType, because Mode can also be meaningfully applied on nominal data
  override def inputSchema: StructType =
  StructType(StructField("value", StringType) :: Nil)

  // This is the internal fields you keep for computing your aggregate.
  // We store the frequency of all the distinct element we encounter for the given attribute in this HashMap
  override def bufferSchema: StructType = StructType(
    StructField("frequencyMap", DataTypes.createMapType(StringType, LongType)) :: Nil
  )

  // This is the output type of your aggregation function.
  override def dataType: DataType = StringType

  override def deterministic: Boolean = true

  // This is the initial value for the buffer schema.
  override def initialize(buffer: MutableAggregationBuffer): Unit = {
    buffer(0) = Map[String, Long]()
  }

  // This is how to update your buffer schema given an input.
  override def update(buffer: MutableAggregationBuffer, input: Row): Unit = {
    buffer(0) = buffer.getAs[Map[String, Long]](0) |+| Map(input.getAs[String](0) -> 1L)
  }

  // This is how you merge two objects with the bufferSchema type.
  override def merge(buffer1: MutableAggregationBuffer, buffer2: Row): Unit = {
    buffer1(0) = buffer1.getAs[Map[String, Long]](0) |+| buffer2.getAs[Map[String, Long]](0)
  }

  // This is where you output the final value, given the final value of your bufferSchema.
  override def evaluate(buffer: Row): String = {
    buffer.getAs[Map[String, Long]](0).maxBy(_._2)._1
  }
 }
diff --git a/MostCommonValue_NoScalaZ.scala b/MostCommonValue_NoScalaZ.scala
 package org.anish.spark.mostcommonvalue

 import org.apache.spark.sql.Row
 import org.apache.spark.sql.expressions.{MutableAggregationBuffer, UserDefinedAggregateFunction}
 import org.apache.spark.sql.types._

 /**
  * Spark User Defined Aggregate Function to calculate the most frequent value in a column. This is similar to
  * Statistical Mode. When there are two random values, this function selects any one. When calculating mode, both
  * these values together is considered as mode.
  *
  * Usage:
  *
  * DataFrame / DataSet DSL
  * val mostCommonValue = new MostCommonValue
  * df.groupBy("group_id").agg(mostCommonValue(col("mode_column")), mostCommonValue(col("city")))
  *
  * Spark SQL:
  * sqlContext.udf.register("mode", new MostCommonValue)
  * %sql
  * -- Use a group_by statement and call the UDAF.
  * select group_id, mode(id) from table group by group_id
  *
  * Reference: https://docs.databricks.com/spark/latest/spark-sql/udaf-scala.html
  *
  * This version doesn't use the ScalaZ library
  *
  * Created by anish on 26/05/17.
  */
 class MostCommonValue_NoScalaz extends UserDefinedAggregateFunction {

  // This is the input fields for your aggregate function.
  // We use StringType, because Mode can also be meaningfully applied on nominal data
  override def inputSchema: StructType =
  StructType(StructField("value", StringType) :: Nil)

  // This is the internal fields you keep for computing your aggregate.
  // We store the frequency of all the distinct element we encounter for the given attribute in this HashMap
  override def bufferSchema: StructType = StructType(
    StructField("frequencyMap", DataTypes.createMapType(StringType, LongType)) :: Nil
  )

  // This is the output type of your aggregation function.
  override def dataType: DataType = StringType

  override def deterministic: Boolean = true

  // This is the initial value for the buffer schema.
  override def initialize(buffer: MutableAggregationBuffer): Unit = {
    buffer(0) = Map[String, Long]()
  }

  // This is how to update your buffer schema given an input.
  override def update(buffer: MutableAggregationBuffer, input: Row): Unit = {
    val inpString = input.getAs[String](0)
    val existingMap = buffer.getAs[Map[String, Long]](0)
    buffer(0) = existingMap + (if (existingMap.contains(inpString)) inpString -> (existingMap(inpString) + 1) else inpString -> 1L)
  }

  // This is how you merge two objects with the bufferSchema type.
  override def merge(buffer1: MutableAggregationBuffer, buffer2: Row): Unit = {
    val map1 = buffer1.getAs[Map[String, Long]](0)
    val map2 = buffer2.getAs[Map[String, Long]](0)
    buffer1(0) =  map1 ++ map2.map{ case (k,v) => k -> (v + map1.getOrElse(k,0L)) }
  }

  // This is where you output the final value, given the final value of your bufferSchema.
  override def evaluate(buffer: Row): String = {
    buffer.getAs[Map[String, Long]](0).maxBy(_._2)._1
  }
 }
	package org.anish.spark.mostcommonvalue

	import org.apache.spark.sql.Row
	import org.apache.spark.sql.expressions.{MutableAggregationBuffer, UserDefinedAggregateFunction}
	import org.apache.spark.sql.types._

	import scalaz.Scalaz._

	/**
	* Spark User Defined Aggregate Function to calculate the most frequent value in a column. This is similar to
	* Statistical Mode. When there are two random values, this function selects any one. When calculating mode, both
	* these values together is considered as mode.
	*
	* Usage:
	*
	* DataFrame / DataSet DSL
	* val mostCommonValue = new MostCommonValue
	* df.groupBy("group_id").agg(mostCommonValue(col("mode_column")), mostCommonValue(col("city")))
	*
	* Spark SQL:
	* sqlContext.udf.register("mode", new MostCommonValue)
	* %sql
	* -- Use a group_by statement and call the UDAF.
	* select group_id, mode(id) from table group by group_id
	*
	* Reference: https://docs.databricks.com/spark/latest/spark-sql/udaf-scala.html
	*
	* Created by anish on 26/05/17.
	*/
	class MostCommonValue extends UserDefinedAggregateFunction {

	// This is the input fields for your aggregate function.
	// We use StringType, because Mode can also be meaningfully applied on nominal data
	override def inputSchema: StructType =
	StructType(StructField("value", StringType) :: Nil)

	// This is the internal fields you keep for computing your aggregate.
	// We store the frequency of all the distinct element we encounter for the given attribute in this HashMap
	override def bufferSchema: StructType = StructType(
	StructField("frequencyMap", DataTypes.createMapType(StringType, LongType)) :: Nil
	)

	// This is the output type of your aggregation function.
	override def dataType: DataType = StringType

	override def deterministic: Boolean = true

	// This is the initial value for the buffer schema.
	override def initialize(buffer: MutableAggregationBuffer): Unit = {
	buffer(0) = Map[String, Long]()
	}

	// This is how to update your buffer schema given an input.
	override def update(buffer: MutableAggregationBuffer, input: Row): Unit = {
	buffer(0) = buffer.getAs[Map[String, Long]](0) \|+\| Map(input.getAs[String](0) -> 1L)
	}

	// This is how you merge two objects with the bufferSchema type.
	override def merge(buffer1: MutableAggregationBuffer, buffer2: Row): Unit = {
	buffer1(0) = buffer1.getAs[Map[String, Long]](0) \|+\| buffer2.getAs[Map[String, Long]](0)
	}

	// This is where you output the final value, given the final value of your bufferSchema.
	override def evaluate(buffer: Row): String = {
	buffer.getAs[Map[String, Long]](0).maxBy(_._2)._1
	}
	}
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