Java Spark Dataframe API (1.4.1) 中未定义 max() 和 sum() 的方法
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Methods of max() and sum() undefined in the Java Spark Dataframe API (1.4.1)
提问by Jingyu Zhang
Putting sample code of DataFrame.groupBy()into my code, but it shown the methods of max()and sum()undefined.
将 的示例代码DataFrame.groupBy()放入我的代码中，但它显示了max()和sum()未定义的方法。
df.groupBy("department").agg(max("age"), sum("expense"));
Which Java package should I import if I want to use max()and sum()method?
如果我想使用max()和sum()方法，我应该导入哪个 Java 包？
Is the Syntax correct of this sample code?
此示例代码的语法是否正确？
回答by vishak
The import didn't work for me. Eclipse IDE still showed the compilation error.
导入对我不起作用。Eclipse IDE 仍然显示编译错误。
But the following method call worked
但以下方法调用有效
df.groupBy("Gender").agg(org.apache.spark.sql.functions.max(df.col("Id")), org.apache.spark.sql.functions.sum(df.col("Income")));
In case the aggregation involves only one field, we can also use the following syntax,
如果聚合只涉及一个字段，我们还可以使用以下语法，
df.groupBy("Gender").max("Income");
回答by Ganesh Krishnan
import static org.apache.spark.sql.functions.*
Try this to import all functions including maxand sum
试试这个导入所有功能，包括max和sum
回答by Niemand
Try import org.apache.spark.sql.functions._
尝试 import org.apache.spark.sql.functions._
EDIT.
编辑。
From what I've noticed you are using scala syntax, trying to acces columns via apply method. For Java, you have to pass columns like with .colmethod this:
从我注意到您正在使用 scala 语法，尝试通过 apply 方法访问列。对于 Java，您必须像这样传递列.col：
df.groupBy("department").agg(max(df.col("age")), sum(df.col("expense")));
See Java example here
请参阅此处的Java 示例
回答by Aron_dc
It seems you're searching for "org.apache.spark.sql.GroupedData"
您似乎正在搜索“org.apache.spark.sql.GroupedData”
To use them in your code like you've written it, you'll need a static import.
要像编写代码一样在代码中使用它们，您需要静态导入。
Always try to have a look at the API descriptions first.
始终尝试先查看 API 描述。
