如何在 spark-shell / pyspark 中打印出 RDD 的片段？

Question

在 spark-shell 中工作时，我经常想检查 RDD（类似于在 unix 中使用 head）。

例如：

scala> val readmeFile = sc.textFile("input/tmp/README.md")
scala> // how to inspect the readmeFile?

和...

scala> val linesContainingSpark = readmeFile.filter(line => line.contains("Spark"))
scala> // how to inspect linesContainingSpark?

Answer 1

我找到了如何做到这一点 (here) 并且认为这对其他用户有用，所以在这里分享。 take(x) 选择前 x 项并 foreach 打印它们：

scala> val readmeFile = sc.textFile("input/tmp/README.md")
scala> readmeFile.take(5).foreach(println)
# Apache Spark

Spark is a fast and general cluster computing system for Big Data. It provides
high-level APIs in Scala, Java, and Python, and an optimized engine that
supports general computation graphs for data analysis. It also supports a

和...

scala> val linesContainingSpark = readmeFile.filter(line => line.contains("Spark"))
scala> linesContainingSpark.take(5).foreach(println)
# Apache Spark
Spark is a fast and general cluster computing system for Big Data. It provides
rich set of higher-level tools including Spark SQL for SQL and structured
and Spark Streaming.
You can find the latest Spark documentation, including a programming

---

下面的示例是等效的，但使用的是 pyspark：

>>> readmeFile = sc.textFile("input/tmp/README.md")
>>> for line in readmeFile.take(5): print line
... 
# Apache Spark

Spark is a fast and general cluster computing system for Big Data. It provides
high-level APIs in Scala, Java, and Python, and an optimized engine that
supports general computation graphs for data analysis. It also supports a

和

>>> linesContainingSpark = readmeFile.filter(lambda line: "Spark" in line)
>>> for line in linesContainingSpark.take(5): print line
... 
# Apache Spark
Spark is a fast and general cluster computing system for Big Data. It provides
rich set of higher-level tools including Spark SQL for SQL and structured
and Spark Streaming.
You can find the latest Spark documentation, including a programming