Add comments and doc. Move some classes to the right places.

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/aggregate2/aggregates.scala

@@ -279,77 +279,5 @@ case class Average(child: Expression) extends AlgebraicAggregate {
   override def children: Seq[Expression] = child :: Nil
 }
 
-abstract class AggregationBuffer(
-    toCatalystConverters: Array[Any => Any],
-    toScalaConverters: Array[Any => Any],
-    bufferOffset: Int)
-  extends Row {
 
-  override def length: Int = toCatalystConverters.length
 
-  protected val offsets: Array[Int] = {
-    val newOffsets = new Array[Int](length)
-    var i = 0
-    while (i < newOffsets.length) {
-      newOffsets(i) = bufferOffset + i
-      i += 1
-    }
-    newOffsets
-  }
-}
-
-class MutableAggregationBuffer(
-    toCatalystConverters: Array[Any => Any],
-    toScalaConverters: Array[Any => Any],
-    bufferOffset: Int,
-    var underlyingBuffer: MutableRow)
-  extends AggregationBuffer(toCatalystConverters, toScalaConverters, bufferOffset) {
-
-  override def apply(i: Int): Any = {
-    if (i >= length || i < 0) {
-      throw new IllegalArgumentException(
-        s"Could not access ${i}th value in this buffer because it only has $length values.")
-    }
-    toScalaConverters(i)(underlyingBuffer(offsets(i)))
-  }
-
-  def update(i: Int, value: Any): Unit = {
-    if (i >= length || i < 0) {
-      throw new IllegalArgumentException(
-        s"Could not update ${i}th value in this buffer because it only has $length values.")
-    }
-    underlyingBuffer.update(offsets(i), toCatalystConverters(i)(value))
-  }
-
-  override def copy(): MutableAggregationBuffer = {
-    new MutableAggregationBuffer(
-      toCatalystConverters,
-      toScalaConverters,
-      bufferOffset,
-      underlyingBuffer)
-  }
-}
-
-class InputAggregationBuffer(
-    toCatalystConverters: Array[Any => Any],
-    toScalaConverters: Array[Any => Any],
-    bufferOffset: Int,
-    var underlyingInputBuffer: Row)
-  extends AggregationBuffer(toCatalystConverters, toScalaConverters, bufferOffset) {
-
-  override def apply(i: Int): Any = {
-    if (i >= length || i < 0) {
-      throw new IllegalArgumentException(
-        s"Could not access ${i}th value in this buffer because it only has $length values.")
-    }
-    toScalaConverters(i)(underlyingInputBuffer(offsets(i)))
-  }
-
-  override def copy(): InputAggregationBuffer = {
-    new InputAggregationBuffer(
-      toCatalystConverters,
-      toScalaConverters,
-      bufferOffset,
-      underlyingInputBuffer)
-  }
-}

sql/core/src/main/scala/org/apache/spark/sql/UDAFRegistration.scala

@@ -19,7 +19,7 @@ package org.apache.spark.sql
 
 import org.apache.spark.Logging
 import org.apache.spark.sql.catalyst.expressions.{Expression}
-import org.apache.spark.sql.execution.expressions.aggregate2.{ScalaUDAF, UserDefinedAggregateFunction}
+import org.apache.spark.sql.expressions.aggregate2.{ScalaUDAF, UserDefinedAggregateFunction}
 
 
 class UDAFRegistration private[sql] (sqlContext: SQLContext) extends Logging {