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

Answer 1

I had similar issue where i had to save the contents of the dataframe to a csv file of name which i defined. df.write("csv").save("<my-path>") was creating directory than file. So have to come up with the following solutions. Most of the code is taken from the following dataframe-to-csv with little modifications to the logic.

def saveDfToCsv(df: DataFrame, tsvOutput: String, sep: String = ",", header: Boolean = false): Unit = {
    val tmpParquetDir = "Posts.tmp.parquet"

    df.repartition(1).write.
        format("com.databricks.spark.csv").
        option("header", header.toString).
        option("delimiter", sep).
        save(tmpParquetDir)

    val dir = new File(tmpParquetDir)
    val newFileRgex = tmpParquetDir + File.separatorChar + ".part-00000.*.csv"
    val tmpTsfFile = dir.listFiles.filter(_.toPath.toString.matches(newFileRgex))(0).toString
    (new File(tmpTsvFile)).renameTo(new File(tsvOutput))

    dir.listFiles.foreach( f => f.delete )
    dir.delete
    }

Answer 2

I had similar problem. I needed to write down csv file on driver while I was connect to cluster in client mode.

I wanted to reuse the same CSV parsing code as Apache Spark to avoid potential errors.

I checked spark-csv code and found code responsible for converting dataframe into raw csv RDD[String] in com.databricks.spark.csv.CsvSchemaRDD.

Sadly it is hardcoded with sc.textFile and the end of relevant method.

I copy-pasted that code and removed last lines with sc.textFile and returned RDD directly instead.

My code:

/*
  This is copypasta from com.databricks.spark.csv.CsvSchemaRDD
  Spark's code has perfect method converting Dataframe -> raw csv RDD[String]
  But in last lines of that method it's hardcoded against writing as text file -
  for our case we need RDD.
 */
object DataframeToRawCsvRDD {

  val defaultCsvFormat = com.databricks.spark.csv.defaultCsvFormat

  def apply(dataFrame: DataFrame, parameters: Map[String, String] = Map())
           (implicit ctx: ExecutionContext): RDD[String] = {
    val delimiter = parameters.getOrElse("delimiter", ",")
    val delimiterChar = if (delimiter.length == 1) {
      delimiter.charAt(0)
    } else {
      throw new Exception("Delimiter cannot be more than one character.")
    }

    val escape = parameters.getOrElse("escape", null)
    val escapeChar: Character = if (escape == null) {
      null
    } else if (escape.length == 1) {
      escape.charAt(0)
    } else {
      throw new Exception("Escape character cannot be more than one character.")
    }

    val quote = parameters.getOrElse("quote", "\"")
    val quoteChar: Character = if (quote == null) {
      null
    } else if (quote.length == 1) {
      quote.charAt(0)
    } else {
      throw new Exception("Quotation cannot be more than one character.")
    }

    val quoteModeString = parameters.getOrElse("quoteMode", "MINIMAL")
    val quoteMode: QuoteMode = if (quoteModeString == null) {
      null
    } else {
      QuoteMode.valueOf(quoteModeString.toUpperCase)
    }

    val nullValue = parameters.getOrElse("nullValue", "null")

    val csvFormat = defaultCsvFormat
      .withDelimiter(delimiterChar)
      .withQuote(quoteChar)
      .withEscape(escapeChar)
      .withQuoteMode(quoteMode)
      .withSkipHeaderRecord(false)
      .withNullString(nullValue)

    val generateHeader = parameters.getOrElse("header", "false").toBoolean
    val headerRdd = if (generateHeader) {
      ctx.sparkContext.parallelize(Seq(
        csvFormat.format(dataFrame.columns.map(_.asInstanceOf[AnyRef]): _*)
      ))
    } else {
      ctx.sparkContext.emptyRDD[String]
    }

    val rowsRdd = dataFrame.rdd.map(row => {
      csvFormat.format(row.toSeq.map(_.asInstanceOf[AnyRef]): _*)
    })

    headerRdd union rowsRdd
  }

}

Answer 3

Writing dataframe to disk as csv is similar read from csv. If you want your result as one file, you can use coalesce.

df.coalesce(1)
      .write
      .option("header","true")
      .option("sep",",")
      .mode("overwrite")
      .csv("output/path")

If your result is an array you should use language specific solution, not spark dataframe api. Because all these kind of results return driver machine.

Answer 4

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.