scala 如何查询 Spark 数据集的列名？
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How to query the column names of a Spark Dataset?
提问by fwc
I have a val ds: Dataset[Double](in Spark 2.0.0), but what is the name of the double-valued column that can be passed to applyor colto convert from this 1-columned Datasetto a Column.
我有一个val ds: Dataset[Double]（在 Spark 2.0.0 中），但是可以传递给apply或col从这个 1 列Dataset转换为Column.
回答by fwc
The column name is "value" as in ds.col("value"). Dataset.schemacontains this information: ds.schema.fields.foreach(x => println(x))
列名是“值”，如ds.col("value"). Dataset.schema包含以下信息：ds.schema.fields.foreach(x => println(x))
回答by Alberto Bonsanto
You could also use DataFrame's method columns, which returns all columns as an Array of Strings.
您还可以使用DataFrame's 方法columns，它将所有列作为字符串数组返回。
case class Person(age: Int, height: Int, weight: Int){
def sum = age + height + weight
}
val df = sc.parallelize(List(Person(1,2,3), Person(4,5,6))).toDF("age", "height", "weight")
df.columns
//res0: Array[String] = Array(age, height, weight)
