scala - How to save a spark DataFrame as csv on disk?

Question

For example, the result of this:

df.filter("project = 'en'").select("title","count").groupBy("title").sum()

would return an Array.

How to save a spark DataFrame as a csv file on disk ?

Answer 1

Apache Spark does not support native CSV output on disk.

You have four available solutions though:

1. You can convert your Dataframe into an RDD :

   def convertToReadableString(r : Row) = ???
   df.rdd.map{ convertToReadableString }.saveAsTextFile(filepath)
   

   This will create a folder filepath. Under the file path, you'll find partitions files (e.g part-000*)

   What I usually do if I want to append all the partitions into a big CSV is

   cat filePath/part* > mycsvfile.csv
   

   Some will use coalesce(1,false) to create one partition from the RDD. It's usually a bad practice, since it may overwhelm the driver by pulling all the data you are collecting to it.

   Note that df.rdd will return an RDD[Row].

2. With Spark <2, you can use databricks spark-csv library:

   • Spark 1.4+:

     df.write.format("com.databricks.spark.csv").save(filepath)
     

   • Spark 1.3:

     df.save(filepath,"com.databricks.spark.csv")
     

3. With Spark 2.x the spark-csv package is not needed as it's included in Spark.

   df.write.format("csv").save(filepath)
   

4. You can convert to local Pandas data frame and use to_csv method (PySpark only).

Note: Solutions 1, 2 and 3 will result in CSV format files (part-*) generated by the underlying Hadoop API that Spark calls when you invoke save. You will have one part- file per partition.