Spark將並行處理數據,但不處理操作。在我的DAG中,我想調用每列的函數,如 Spark processing columns in parallel,每列的值可以獨立於其他列計算。有什麼辦法通過spark-SQL API實現這種並行性?利用窗口函數Spark dynamic DAG is a lot slower and different from hard coded DAG有助於優化DAG,但只能以串行方式執行。spark並行應用函數列
其中包含多一點點信息的例子可以在下面https://github.com/geoHeil/sparkContrastCoding
最低例子發現:
val df = Seq(
(0, "A", "B", "C", "D"),
(1, "A", "B", "C", "D"),
(0, "d", "a", "jkl", "d"),
(0, "d", "g", "C", "D"),
(1, "A", "d", "t", "k"),
(1, "d", "c", "C", "D"),
(1, "c", "B", "C", "D")
).toDF("TARGET", "col1", "col2", "col3TooMany", "col4")
val inputToDrop = Seq("col3TooMany")
val inputToBias = Seq("col1", "col2")
val targetCounts = df.filter(df("TARGET") === 1).groupBy("TARGET").agg(count("TARGET").as("cnt_foo_eq_1"))
val newDF = df.toDF.join(broadcast(targetCounts), Seq("TARGET"), "left")
newDF.cache
def handleBias(df: DataFrame, colName: String, target: String = target) = {
val w1 = Window.partitionBy(colName)
val w2 = Window.partitionBy(colName, target)
df.withColumn("cnt_group", count("*").over(w2))
.withColumn("pre2_" + colName, mean(target).over(w1))
.withColumn("pre_" + colName, coalesce(min(col("cnt_group")/col("cnt_foo_eq_1")).over(w1), lit(0D)))
.drop("cnt_group")
}
val joinUDF = udf((newColumn: String, newValue: String, codingVariant: Int, results: Map[String, Map[String, Seq[Double]]]) => {
results.get(newColumn) match {
case Some(tt) => {
val nestedArray = tt.getOrElse(newValue, Seq(0.0))
if (codingVariant == 0) {
nestedArray.head
} else {
nestedArray.last
}
}
case None => throw new Exception("Column not contained in initial data frame")
}
})
現在,我想我的handleBias
功能適用於所有列,遺憾的是,這是不是並行執行。爲每列
val res = (inputToDrop ++ inputToBias).toSet.foldLeft(newDF) {
(currentDF, colName) =>
{
logger.info("using col " + colName)
handleBias(currentDF, colName)
}
}
.drop("cnt_foo_eq_1")
val combined = ((inputToDrop ++ inputToBias).toSet).foldLeft(res) {
(currentDF, colName) =>
{
currentDF
.withColumn("combined_" + colName, map(col(colName), array(col("pre_" + colName), col("pre2_" + colName))))
}
}
val columnsToUse = combined
.select(combined.columns
.filter(_.startsWith("combined_"))
map (combined(_)): _*)
val newNames = columnsToUse.columns.map(_.split("combined_").last)
val renamed = columnsToUse.toDF(newNames: _*)
val cols = renamed.columns
val localData = renamed.collect
val columnsMap = cols.map { colName =>
colName -> localData.flatMap(_.getAs[Map[String, Seq[Double]]](colName)).toMap
}.toMap