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[英]How to split a spark scala dataframe if number of rows are greater than threshold
[英]Scala: How to join more than one Spark Dataframe by rows?
private def unionAll(dataFrames: Seq[DataFrame], sqlContext: SQLContext): DataFrame = dataFrames match {
case Nil => sqlContext.emptyDataFrame
case head :: Nil => head
case head :: tail => head.unionAll(unionAll(tail, sqlContext))
}
需要第二种情况,以防止尝试将空DF(没有正确的架构)与非空DF合并。
这确实假定如果列表不为空,则所有DataFrame共享相同的架构。
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