java - Spark SQL - DataFrame - 选择 - 转换还是操作？

Question

在 Spark SQL 中(使用 Java API)我有一个 DataFrame。

DataFrame 有一个select 方法。不知是改造还是 Action ？

我只需要一份确认书和一份清楚说明的引用资料。

Answer 1

就是转型。请引用:https://spark.apache.org/docs/2.0.0/api/java/org/apache/spark/sql/Dataset.html

A Dataset is a strongly typed collection of domain-specific objects that can be transformed in parallel using functional or relational operations. Each Dataset also has an untyped view called a DataFrame, which is a Dataset of Row.

Operations available on Datasets are divided into transformations and actions. Transformations are the ones that produce new Datasets, and actions are the ones that trigger computation and return results. Example transformations include map, filter, select, and aggregate (groupBy). Example actions count, show, or writing data out to file systems.