Github user zsxwing commented on a diff in the pull request: https://github.com/apache/spark/pull/16970#discussion_r102391414 --- Diff: sql/core/src/main/scala/org/apache/spark/sql/Dataset.scala --- @@ -1996,7 +1996,7 @@ class Dataset[T] private[sql]( def dropDuplicates(colNames: Seq[String]): Dataset[T] = withTypedPlan { val resolver = sparkSession.sessionState.analyzer.resolver val allColumns = queryExecution.analyzed.output - val groupCols = colNames.flatMap { colName => + val groupCols = colNames.toSet.toSeq.flatMap { (colName: String) => --- End diff -- The results will be same. It's just pretty weird that it depends on the optimizer to remove duplicated columns.
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