将一行转换为 spark scala 中的列表
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Convert a row to a list in spark scala
提问by Mr.cysl
Is that possible to do that? All the data in my dataframe(~1000 cols) are Doubles and I'm wandering whether I could turn a row of data to a list of Doubles?
这样做有可能吗？我的数据框中的所有数据（~1000 列）都是双精度数，我在犹豫是否可以将一行数据转换为双精度数列表？
回答by Psidom
You can use toSeqmethod on the Row and then convert the type from Seq[Any]to Seq[Double](if you are sure the data types of all the columns are Double):
您可以toSeq在 Row 上使用方法，然后将类型从Seq[Any]to转换Seq[Double]（如果您确定所有列的数据类型都是 Double）：
val df = Seq((1.0,2.0),(2.1,2.2)).toDF("A", "B")
// df: org.apache.spark.sql.DataFrame = [A: double, B: double]
df.show
+---+---+
| A| B|
+---+---+
|1.0|2.0|
|2.1|2.2|
+---+---+
df.first.toSeq.asInstanceOf[Seq[Double]]
// res1: Seq[Double] = WrappedArray(1.0, 2.0)
In case you have String type columns, use toSeqand then use mapwith pattern matching to convert the Stringto Double:
如果您有 String 类型的列，请使用toSeq然后map与模式匹配一起使用将String转换为Double：
val df = Seq((1.0,"2.0"),(2.1,"2.2")).toDF("A", "B")
// df: org.apache.spark.sql.DataFrame = [A: double, B: string]
df.first.toSeq.map{
case x: String => x.toDouble
case x: Double => x
}
// res3: Seq[Double] = ArrayBuffer(1.0, 2.0)
回答by Ramesh Maharjan
If you have a dataframewith doubleswhich you want to convert into Listof doubles, then just convert the dataframeinto rddwhich will give you RDD[Row]you can covert this to Listas
如果你有一个dataframe与doubles它要转换成List的doubles，那么就转换dataframe成rdd它会给你RDD[Row]，你可以隐蔽这List是
dataframe.rdd.map(_.toSeq.toList)
You will get list of doubles
你会得到 list of doubles
