Github user hvanhovell commented on a diff in the pull request: https://github.com/apache/spark/pull/7057#discussion_r33641018 --- Diff: sql/core/src/main/scala/org/apache/spark/sql/execution/Window.scala --- @@ -19,17 +19,39 @@ package org.apache.spark.sql.execution import java.util -import org.apache.spark.rdd.RDD +import org.apache.spark.annotation.DeveloperApi import org.apache.spark.sql.catalyst.expressions._ -import org.apache.spark.sql.catalyst.plans.physical.{AllTuples, ClusteredDistribution, Distribution, Partitioning} +import org.apache.spark.sql.catalyst.plans.physical._ +import org.apache.spark.sql.types.IntegerType +import org.apache.spark.rdd.RDD import org.apache.spark.util.collection.CompactBuffer +import scala.collection.mutable /** * :: DeveloperApi :: - * For every row, evaluates `windowExpression` containing Window Functions and attaches - * the results with other regular expressions (presented by `projectList`). - * Evert operator handles a single Window Specification, `windowSpec`. + * This class calculates and outputs (windowed) aggregates over the rows in a single sorted group. + * The aggregates are calculated for each row in the group. An aggregate can take a few forms: + * - Global: The aggregate is calculated for the entire group. Every row has the same value. + * - Rows: The aggregate is calculated based on a subset of the window, and is unique for each + * row and depends on the position of the given row within the window. The group must be sorted + * for this to produce sensible output. Examples are moving averages, running sums and row + * numbers. + * - Range: The aggregate is calculated based on a subset of the window, and is unique for each + * value of the order by clause and depends on its ordering. The group must be sorted for this to + * produce sensible output. + * - Shifted: The aggregate is a displaced value relative to the position of the given row. + * Examples are Lead and Lag. --- End diff -- I agree. There are still a few other documentation inconsistencies, and I'll try to fix those as well.
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