在Scala中将数据帧作为可选功能参数传递 [英] Passing data frame as optional function parameter in Scala
问题描述
有没有一种方法可以将数据帧作为Scala中的可选输入函数参数传递? 例如:
Is there a way that I can pass a data frame as an optional input function parameter in Scala? Ex:
def test(sampleDF: DataFrame = df.sqlContext.emptyDataFrame): DataFrame = {
}
df.test(sampleDF)
尽管我在此处传递了一个有效的数据帧,但始终将其分配给一个空的数据帧,如何避免这种情况?
Though I am passing a valid data frame here , it is always assigned to an empty data frame, how can I avoid this?
推荐答案
是的,您可以将dataframe
作为参数传递给函数
Yes you can pass dataframe
as a parameter to a function
让我们说您有dataframe
作为
import sqlContext.implicits._
val df = Seq(
(1, 2, 3),
(1, 2, 3)
).toDF("col1", "col2", "col3")
是
+----+----+----+
|col1|col2|col3|
+----+----+----+
|1 |2 |3 |
|1 |2 |3 |
+----+----+----+
您可以将其传递给以下函数
you can pass it to a function as below
import org.apache.spark.sql.DataFrame
def test(sampleDF: DataFrame): DataFrame = {
sampleDF.select("col1", "col2") //doing some operation in dataframe
}
val testdf = test(df)
testdf
为
+----+----+
|col1|col2|
+----+----+
|1 |2 |
|1 |2 |
+----+----+
已编辑
正如eliasah指出的那样,@ Garipaso希望使用可选参数.可以通过将函数定义为
As eliasah pointed out that @Garipaso wanted optional argument. This can be done by defining the function as
def test(sampleDF: DataFrame = sqlContext.emptyDataFrame): DataFrame = {
if(sampleDF.count() > 0) sampleDF.select("col1", "col2") //doing some operation in dataframe
else sqlContext.emptyDataFrame
}
如果我们将有效数据框传递为
If we pass a valid dataframe as
test(df).show(false)
它将输出为
+----+----+
|col1|col2|
+----+----+
|1 |2 |
|1 |2 |
+----+----+
但是,如果我们不将参数传递为
But if we don't pass argument as
test().show(false)
我们将获得空的数据框为
we would get empty dataframe as
++
||
++
++
我希望答案会有所帮助
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