DataFrame — Dataset of Rows

Spark SQL introduces a tabular data abstraction called DataFrame. It is designed to ease processing large amount of structured tabular data on Spark infrastructure.

A DataFrame is a data abstraction or a domain-specific language (DSL) for working with structured and semi-structured data, i.e. datasets with a schema. A DataFrame is thus a collection of rows with a schema that is a result of a structured query it describes.

It uses the immutable, in-memory, resilient, distributed and parallel capabilities of RDD, and applies a structure called schema to the data.

Note

In Spark 2.0.0 DataFrame is a mere type alias for Dataset[Row].

type DataFrame = Dataset[Row]

DataFrame is a distributed collection of tabular data organized into rows and named columns. It is conceptually equivalent to a table in a relational database with operations to project (select), filter, intersect, join, group, sort, join, aggregate, or convert to a RDD (consult DataFrame API)

data.groupBy('Product_ID).sum('Score)

Spark SQL borrowed the concept of DataFrame from pandas' DataFrame and made it immutable, parallel (one machine, perhaps with many processors and cores) and distributed (many machines, perhaps with many processors and cores).

Note
Hey, big data consultants, time to help teams migrate the code from pandas' DataFrame into Spark’s DataFrames (at least to PySpark’s DataFrame) and offer services to set up large clusters!

DataFrames in Spark SQL strongly rely on the features of RDD - it’s basically a RDD exposed as structured DataFrame by appropriate operations to handle very big data from the day one. So, petabytes of data should not scare you (unless you’re an administrator to create such clustered Spark environment - contact me when you feel alone with the task).

val df = Seq(("one", 1), ("one", 1), ("two", 1))
  .toDF("word", "count")

scala> df.show
+----+-----+
|word|count|
+----+-----+
| one|    1|
| one|    1|
| two|    1|
+----+-----+

val counted = df.groupBy('word).count

scala> counted.show
+----+-----+
|word|count|
+----+-----+
| two|    1|
| one|    2|
+----+-----+

You can create DataFrames by loading data from structured files (JSON, Parquet, CSV), RDDs, tables in Hive, or external databases (JDBC). You can also create DataFrames from scratch and build upon them (as in the above example). See DataFrame API. You can read any format given you have appropriate Spark SQL extension of DataFrameReader to format the dataset appropriately.

Caution
FIXME Diagram of reading data from sources to create DataFrame

You can execute queries over DataFrames using two approaches:

  • the good ol' SQL - helps migrating from "SQL databases" world into the world of DataFrame in Spark SQL

  • Query DSL - an API that helps ensuring proper syntax at compile time.

DataFrame also allows you to do the following tasks:

DataFrames use the Catalyst query optimizer to produce efficient queries (and so they are supposed to be faster than corresponding RDD-based queries).

Note
Your DataFrames can also be type-safe and moreover further improve their performance through specialized encoders that can significantly cut serialization and deserialization times.

You can enforce types on generic rows and hence bring type safety (at compile time) by encoding rows into type-safe Dataset object. As of Spark 2.0 it is a preferred way of developing Spark applications.

Features of DataFrame

A DataFrame is a collection of "generic" Row instances (as RDD[Row]) and a schema.

Note
Regardless of how you create a DataFrame, it will always be a pair of RDD[Row] and StructType.

Enforcing Types (as method)

DataFrame is a type alias for Dataset[Row]. You can enforce types of the fields using as method.

as gives you a conversion from Dataset[Row] to Dataset[T].

// Create DataFrame of pairs
val df = Seq("hello", "world!").zipWithIndex.map(_.swap).toDF("id", "token")

scala> df.printSchema
root
 |-- id: integer (nullable = false)
 |-- token: string (nullable = true)

scala> val ds = df.as[(Int, String)]
ds: org.apache.spark.sql.Dataset[(Int, String)] = [id: int, token: string]

// It's more helpful to have a case class for the conversion
final case class MyRecord(id: Int, token: String)

scala> val myRecords = df.as[MyRecord]
myRecords: org.apache.spark.sql.Dataset[MyRecord] = [id: int, token: string]

Writing DataFrames to External Storage (write method)

Caution
FIXME

SQLContext, spark, and Spark shell

You use org.apache.spark.sql.SQLContext to build DataFrames and execute SQL queries.

The quickest and easiest way to work with Spark SQL is to use Spark shell and spark object.

scala> spark
res1: org.apache.spark.sql.SQLContext = org.apache.spark.sql.hive.HiveContext@60ae950f

As you may have noticed, spark in Spark shell is actually a org.apache.spark.sql.hive.HiveContext that integrates the Spark SQL execution engine with data stored in Apache Hive.

The Apache Hive™ data warehouse software facilitates querying and managing large datasets residing in distributed storage.

Creating DataFrames from Scratch

Use Spark shell as described in Spark shell.

Using toDF

After you import spark.implicits._ (which is done for you by Spark shell) you may apply toDF method to convert objects to DataFrames.

scala> val df = Seq("I am a DataFrame!").toDF("text")
df: org.apache.spark.sql.DataFrame = [text: string]

Creating DataFrame using Case Classes in Scala

This method assumes the data comes from a Scala case class that will describe the schema.

scala> case class Person(name: String, age: Int)
defined class Person

scala> val people = Seq(Person("Jacek", 42), Person("Patryk", 19), Person("Maksym", 5))
people: Seq[Person] = List(Person(Jacek,42), Person(Patryk,19), Person(Maksym,5))

scala> val df = spark.createDataFrame(people)
df: org.apache.spark.sql.DataFrame = [name: string, age: int]

scala> df.show
+------+---+
|  name|age|
+------+---+
| Jacek| 42|
|Patryk| 19|
|Maksym|  5|
+------+---+

Custom DataFrame Creation using createDataFrame

SQLContext offers a family of createDataFrame operations.

scala> val lines = sc.textFile("Cartier+for+WinnersCurse.csv")
lines: org.apache.spark.rdd.RDD[String] = MapPartitionsRDD[3] at textFile at <console>:24

scala> val headers = lines.first
headers: String = auctionid,bid,bidtime,bidder,bidderrate,openbid,price

scala> import org.apache.spark.sql.types.{StructField, StringType}
import org.apache.spark.sql.types.{StructField, StringType}

scala> val fs = headers.split(",").map(f => StructField(f, StringType))
fs: Array[org.apache.spark.sql.types.StructField] = Array(StructField(auctionid,StringType,true), StructField(bid,StringType,true), StructField(bidtime,StringType,true), StructField(bidder,StringType,true), StructField(bidderrate,StringType,true), StructField(openbid,StringType,true), StructField(price,StringType,true))

scala> import org.apache.spark.sql.types.StructType
import org.apache.spark.sql.types.StructType

scala> val schema = StructType(fs)
schema: org.apache.spark.sql.types.StructType = StructType(StructField(auctionid,StringType,true), StructField(bid,StringType,true), StructField(bidtime,StringType,true), StructField(bidder,StringType,true), StructField(bidderrate,StringType,true), StructField(openbid,StringType,true), StructField(price,StringType,true))

scala> val noheaders = lines.filter(_ != header)
noheaders: org.apache.spark.rdd.RDD[String] = MapPartitionsRDD[10] at filter at <console>:33

scala> import org.apache.spark.sql.Row
import org.apache.spark.sql.Row

scala> val rows = noheaders.map(_.split(",")).map(a => Row.fromSeq(a))
rows: org.apache.spark.rdd.RDD[org.apache.spark.sql.Row] = MapPartitionsRDD[12] at map at <console>:35

scala> val auctions = spark.createDataFrame(rows, schema)
auctions: org.apache.spark.sql.DataFrame = [auctionid: string, bid: string, bidtime: string, bidder: string, bidderrate: string, openbid: string, price: string]

scala> auctions.printSchema
root
 |-- auctionid: string (nullable = true)
 |-- bid: string (nullable = true)
 |-- bidtime: string (nullable = true)
 |-- bidder: string (nullable = true)
 |-- bidderrate: string (nullable = true)
 |-- openbid: string (nullable = true)
 |-- price: string (nullable = true)

scala> auctions.dtypes
res28: Array[(String, String)] = Array((auctionid,StringType), (bid,StringType), (bidtime,StringType), (bidder,StringType), (bidderrate,StringType), (openbid,StringType), (price,StringType))

scala> auctions.show(5)
+----------+----+-----------+-----------+----------+-------+-----+
| auctionid| bid|    bidtime|     bidder|bidderrate|openbid|price|
+----------+----+-----------+-----------+----------+-------+-----+
|1638843936| 500|0.478368056|  kona-java|       181|    500| 1625|
|1638843936| 800|0.826388889|     doc213|        60|    500| 1625|
|1638843936| 600|3.761122685|       zmxu|         7|    500| 1625|
|1638843936|1500|5.226377315|carloss8055|         5|    500| 1625|
|1638843936|1600|   6.570625|    jdrinaz|         6|    500| 1625|
+----------+----+-----------+-----------+----------+-------+-----+
only showing top 5 rows

Loading data from structured files

Creating DataFrame from CSV file

Let’s start with an example in which schema inference relies on a custom case class in Scala.

scala> val lines = sc.textFile("Cartier+for+WinnersCurse.csv")
lines: org.apache.spark.rdd.RDD[String] = MapPartitionsRDD[3] at textFile at <console>:24

scala> val header = lines.first
header: String = auctionid,bid,bidtime,bidder,bidderrate,openbid,price

scala> lines.count
res3: Long = 1349

scala> case class Auction(auctionid: String, bid: Float, bidtime: Float, bidder: String, bidderrate: Int, openbid: Float, price: Float)
defined class Auction

scala> val noheader = lines.filter(_ != header)
noheader: org.apache.spark.rdd.RDD[String] = MapPartitionsRDD[53] at filter at <console>:31

scala> val auctions = noheader.map(_.split(",")).map(r => Auction(r(0), r(1).toFloat, r(2).toFloat, r(3), r(4).toInt, r(5).toFloat, r(6).toFloat))
auctions: org.apache.spark.rdd.RDD[Auction] = MapPartitionsRDD[59] at map at <console>:35

scala> val df = auctions.toDF
df: org.apache.spark.sql.DataFrame = [auctionid: string, bid: float, bidtime: float, bidder: string, bidderrate: int, openbid: float, price: float]

scala> df.printSchema
root
 |-- auctionid: string (nullable = true)
 |-- bid: float (nullable = false)
 |-- bidtime: float (nullable = false)
 |-- bidder: string (nullable = true)
 |-- bidderrate: integer (nullable = false)
 |-- openbid: float (nullable = false)
 |-- price: float (nullable = false)

scala> df.show
+----------+------+----------+-----------------+----------+-------+------+
| auctionid|   bid|   bidtime|           bidder|bidderrate|openbid| price|
+----------+------+----------+-----------------+----------+-------+------+
|1638843936| 500.0|0.47836804|        kona-java|       181|  500.0|1625.0|
|1638843936| 800.0| 0.8263889|           doc213|        60|  500.0|1625.0|
|1638843936| 600.0| 3.7611227|             zmxu|         7|  500.0|1625.0|
|1638843936|1500.0| 5.2263775|      carloss8055|         5|  500.0|1625.0|
|1638843936|1600.0|  6.570625|          jdrinaz|         6|  500.0|1625.0|
|1638843936|1550.0| 6.8929167|      carloss8055|         5|  500.0|1625.0|
|1638843936|1625.0| 6.8931136|      carloss8055|         5|  500.0|1625.0|
|1638844284| 225.0|  1.237419|dre_313@yahoo.com|         0|  200.0| 500.0|
|1638844284| 500.0| 1.2524074|        njbirdmom|        33|  200.0| 500.0|
|1638844464| 300.0| 1.8111342|          aprefer|        58|  300.0| 740.0|
|1638844464| 305.0| 3.2126737|        19750926o|         3|  300.0| 740.0|
|1638844464| 450.0| 4.1657987|         coharley|        30|  300.0| 740.0|
|1638844464| 450.0| 6.7363195|        adammurry|         5|  300.0| 740.0|
|1638844464| 500.0| 6.7364697|        adammurry|         5|  300.0| 740.0|
|1638844464|505.78| 6.9881945|        19750926o|         3|  300.0| 740.0|
|1638844464| 551.0| 6.9896526|        19750926o|         3|  300.0| 740.0|
|1638844464| 570.0| 6.9931483|        19750926o|         3|  300.0| 740.0|
|1638844464| 601.0| 6.9939003|        19750926o|         3|  300.0| 740.0|
|1638844464| 610.0|  6.994965|        19750926o|         3|  300.0| 740.0|
|1638844464| 560.0| 6.9953704|            ps138|         5|  300.0| 740.0|
+----------+------+----------+-----------------+----------+-------+------+
only showing top 20 rows

Creating DataFrame from CSV files using spark-csv module

You’re going to use spark-csv module to load data from a CSV data source that handles proper parsing and loading.

Note
Support for CSV data sources is available by default in Spark 2.0.0. No need for an external module.

Start the Spark shell using --packages option as follows:

➜  spark git:(master) ✗ ./bin/spark-shell --packages com.databricks:spark-csv_2.11:1.2.0
Ivy Default Cache set to: /Users/jacek/.ivy2/cache
The jars for the packages stored in: /Users/jacek/.ivy2/jars
:: loading settings :: url = jar:file:/Users/jacek/dev/oss/spark/assembly/target/scala-2.11/spark-assembly-1.5.0-SNAPSHOT-hadoop2.7.1.jar!/org/apache/ivy/core/settings/ivysettings.xml
com.databricks#spark-csv_2.11 added as a dependency

scala> val df = spark.read.format("com.databricks.spark.csv").option("header", "true").load("Cartier+for+WinnersCurse.csv")
df: org.apache.spark.sql.DataFrame = [auctionid: string, bid: string, bidtime: string, bidder: string, bidderrate: string, openbid: string, price: string]

scala> df.printSchema
root
 |-- auctionid: string (nullable = true)
 |-- bid: string (nullable = true)
 |-- bidtime: string (nullable = true)
 |-- bidder: string (nullable = true)
 |-- bidderrate: string (nullable = true)
 |-- openbid: string (nullable = true)
 |-- price: string (nullable = true)

 scala> df.show
 +----------+------+-----------+-----------------+----------+-------+-----+
 | auctionid|   bid|    bidtime|           bidder|bidderrate|openbid|price|
 +----------+------+-----------+-----------------+----------+-------+-----+
 |1638843936|   500|0.478368056|        kona-java|       181|    500| 1625|
 |1638843936|   800|0.826388889|           doc213|        60|    500| 1625|
 |1638843936|   600|3.761122685|             zmxu|         7|    500| 1625|
 |1638843936|  1500|5.226377315|      carloss8055|         5|    500| 1625|
 |1638843936|  1600|   6.570625|          jdrinaz|         6|    500| 1625|
 |1638843936|  1550|6.892916667|      carloss8055|         5|    500| 1625|
 |1638843936|  1625|6.893113426|      carloss8055|         5|    500| 1625|
 |1638844284|   225|1.237418982|dre_313@yahoo.com|         0|    200|  500|
 |1638844284|   500|1.252407407|        njbirdmom|        33|    200|  500|
 |1638844464|   300|1.811134259|          aprefer|        58|    300|  740|
 |1638844464|   305|3.212673611|        19750926o|         3|    300|  740|
 |1638844464|   450|4.165798611|         coharley|        30|    300|  740|
 |1638844464|   450|6.736319444|        adammurry|         5|    300|  740|
 |1638844464|   500|6.736469907|        adammurry|         5|    300|  740|
 |1638844464|505.78|6.988194444|        19750926o|         3|    300|  740|
 |1638844464|   551|6.989652778|        19750926o|         3|    300|  740|
 |1638844464|   570|6.993148148|        19750926o|         3|    300|  740|
 |1638844464|   601|6.993900463|        19750926o|         3|    300|  740|
 |1638844464|   610|6.994965278|        19750926o|         3|    300|  740|
 |1638844464|   560| 6.99537037|            ps138|         5|    300|  740|
 +----------+------+-----------+-----------------+----------+-------+-----+
 only showing top 20 rows

Reading Data from External Data Sources (read method)

You can create DataFrames by loading data from structured files (JSON, Parquet, CSV), RDDs, tables in Hive, or external databases (JDBC) using SQLContext.read method.

read: DataFrameReader

read returns a DataFrameReader instance.

Among the supported structured data (file) formats are (consult Specifying Data Format (format method) for DataFrameReader):

  • JSON

  • parquet

  • JDBC

  • ORC

  • Tables in Hive and any JDBC-compliant database

  • libsvm

val reader = spark.read
r: org.apache.spark.sql.DataFrameReader = org.apache.spark.sql.DataFrameReader@59e67a18

reader.parquet("file.parquet")
reader.json("file.json")
reader.format("libsvm").load("sample_libsvm_data.txt")

Querying DataFrame

Note
Spark SQL offers a Pandas-like Query DSL.

Using Query DSL

You can select specific columns using select method.

Note
This variant (in which you use stringified column names) can only select existing columns, i.e. you cannot create new ones using select expressions.
scala> predictions.printSchema
root
 |-- id: long (nullable = false)
 |-- topic: string (nullable = true)
 |-- text: string (nullable = true)
 |-- label: double (nullable = true)
 |-- words: array (nullable = true)
 |    |-- element: string (containsNull = true)
 |-- features: vector (nullable = true)
 |-- rawPrediction: vector (nullable = true)
 |-- probability: vector (nullable = true)
 |-- prediction: double (nullable = true)

scala> predictions.select("label", "words").show
+-----+-------------------+
|label|              words|
+-----+-------------------+
|  1.0|     [hello, math!]|
|  0.0| [hello, religion!]|
|  1.0|[hello, phy, ic, !]|
+-----+-------------------+
scala> auctions.groupBy("bidder").count().show(5)
+--------------------+-----+
|              bidder|count|
+--------------------+-----+
|    dennisthemenace1|    1|
|            amskymom|    5|
| nguyenat@san.rr.com|    4|
|           millyjohn|    1|
|ykelectro@hotmail...|    2|
+--------------------+-----+
only showing top 5 rows

In the following example you query for the top 5 of the most active bidders.

Note the tiny $ and desc together with the column name to sort the rows by.

scala> auctions.groupBy("bidder").count().sort($"count".desc).show(5)
+------------+-----+
|      bidder|count|
+------------+-----+
|    lass1004|   22|
|  pascal1666|   19|
|     freembd|   17|
|restdynamics|   17|
|   happyrova|   17|
+------------+-----+
only showing top 5 rows

scala> import org.apache.spark.sql.functions._
import org.apache.spark.sql.functions._

scala> auctions.groupBy("bidder").count().sort(desc("count")).show(5)
+------------+-----+
|      bidder|count|
+------------+-----+
|    lass1004|   22|
|  pascal1666|   19|
|     freembd|   17|
|restdynamics|   17|
|   happyrova|   17|
+------------+-----+
only showing top 5 rows
scala> df.select("auctionid").distinct.count
res88: Long = 97

scala> df.groupBy("bidder").count.show
+--------------------+-----+
|              bidder|count|
+--------------------+-----+
|    dennisthemenace1|    1|
|            amskymom|    5|
| nguyenat@san.rr.com|    4|
|           millyjohn|    1|
|ykelectro@hotmail...|    2|
|   shetellia@aol.com|    1|
|              rrolex|    1|
|            bupper99|    2|
|           cheddaboy|    2|
|             adcc007|    1|
|           varvara_b|    1|
|            yokarine|    4|
|          steven1328|    1|
|              anjara|    2|
|              roysco|    1|
|lennonjasonmia@ne...|    2|
|northwestportland...|    4|
|             bosspad|   10|
|        31strawberry|    6|
|          nana-tyler|   11|
+--------------------+-----+
only showing top 20 rows

Using SQL

Register a DataFrame as a named temporary table to run SQL.

scala> df.registerTempTable("auctions") (1)

scala> val sql = spark.sql("SELECT count(*) AS count FROM auctions")
sql: org.apache.spark.sql.DataFrame = [count: bigint]
  1. Register a temporary table so SQL queries make sense

You can execute a SQL query on a DataFrame using sql operation, but before the query is executed it is optimized by Catalyst query optimizer. You can print the physical plan for a DataFrame using the explain operation.

scala> sql.explain
== Physical Plan ==
TungstenAggregate(key=[], functions=[(count(1),mode=Final,isDistinct=false)], output=[count#148L])
 TungstenExchange SinglePartition
  TungstenAggregate(key=[], functions=[(count(1),mode=Partial,isDistinct=false)], output=[currentCount#156L])
   TungstenProject
    Scan PhysicalRDD[auctionid#49,bid#50,bidtime#51,bidder#52,bidderrate#53,openbid#54,price#55]

scala> sql.show
+-----+
|count|
+-----+
| 1348|
+-----+

scala> val count = sql.collect()(0).getLong(0)
count: Long = 1348

Filtering

scala> df.show
+----+---------+-----+
|name|productId|score|
+----+---------+-----+
| aaa|      100| 0.12|
| aaa|      200| 0.29|
| bbb|      200| 0.53|
| bbb|      300| 0.42|
+----+---------+-----+

scala> df.filter($"name".like("a%")).show
+----+---------+-----+
|name|productId|score|
+----+---------+-----+
| aaa|      100| 0.12|
| aaa|      200| 0.29|
+----+---------+-----+

Handling data in Avro format

Use custom serializer using spark-avro.

Run Spark shell with --packages com.databricks:spark-avro_2.11:2.0.0 (see 2.0.0 artifact is not in any public maven repo why --repositories is required).

./bin/spark-shell --packages com.databricks:spark-avro_2.11:2.0.0 --repositories "http://dl.bintray.com/databricks/maven"

And then…​

val fileRdd = sc.textFile("README.md")
val df = fileRdd.toDF

import org.apache.spark.sql.SaveMode

val outputF = "test.avro"
df.write.mode(SaveMode.Append).format("com.databricks.spark.avro").save(outputF)

See org.apache.spark.sql.SaveMode (and perhaps org.apache.spark.sql.SaveMode from Scala’s perspective).

val df = spark.read.format("com.databricks.spark.avro").load("test.avro")

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