Apache Spark on Scala basic example

Ryan Lindbeck
7 min readMay 14, 2024

Apache Spark is a unified analytics engine for large-scale data processing. Scala is a programming language that combines object-oriented and functional programming in one concise, high-level language. Combined they are used to create powerful data applications in the ETL/ELT, ML and AI universes.

This article will walk you through a basic example of setting up and performing fundamental data operations that will help get your feet wet with modern big data engineering concepts.

The full code base for this example is published here if you would like to go straight to the source.

Also you can watch me walk through the code on Youtube.

1. Set up Scala Build Tool (sbt).

Download and install sbt.

sbt is Scala’s interactive build tool. It will allow you run your app, define project dependencies, apply plugins and more. Review the sbt docs for more info on how to use it.

After you have downloaded and installed it, run sbt help to ensure that it is installed properly.

2. Create new project directory.

Create a new directory called spark-scala-examples and navigate into it from your terminal. If you'd like, you can name this directory whatever you want. We will refer to this as the root of your project.

mkdir spark-scala-examples && cd spark-scala-examples

3. Open project in Visual Studio Code.

If you don’t already have it installed, go here and install it for your operating system.

Visual Studio Code (VS Code) is an Integrated Development Environment tool, or IDE for short. This is what we will use to edit our code files for this project.

You may choose to use other IDE’s if you want. Other popular IDE’s include IntelliJ and Atom.

4. Create SBT build file.

From within Visual Studio Code, create a new file inside the root directory called build.sbt and add the following code to it.

ThisBuild / scalaVersion := "2.12.17"
ThisBuild / organization := "com.inndevers"

val sparkVersion = "3.2.2"

lazy val root = (project in file("."))
.settings(
name := "SparkScalaExamples",
libraryDependencies += "org.apache.spark" %% "spark-core" % sparkVersion,
libraryDependencies += "org.apache.spark" %% "spark-sql" % sparkVersion,
libraryDependencies += "org.scalatest" %% "scalatest" % "3.2.7" % Test
)

This file should stay at the root of your project. Let's review some of the key lines in here.

  • Line 1: Indicates the version of Scala you will use for this projects. In this case, it’s 2.12.17.
  • Line 2: Indicates your package organization. You can change this to whatever you’d like.
  • Line 4: Indicates the version fo Spark we will use. In this case, it’s 3.2.2.
  • Line 6: Initiates the root project settings.
  • Line 8: Configures the name of the app. You can make this whatever you’d like.
  • Lines 9–11: These identify the dependencies required for our project. As you can see we have spark-core and spark-sql. We also have scalatest which we do not use in this demo, however it's always good to add when you're ready to jump into Unit Testing.

5. Create main class.

Create the main Scala class that will be the entry point into your app. We'll call this class BasicExample.scala. But first, lets create the app directory structure.

From within the root of your project, create the following directory structure.

.
├── src
│ └── main
│ └── scala
│ └── basic
│ └── BasicExample.scala
└── build.sbt

Then, create a file named BasicExample.scala inside of the basic folder and add the following code to it.

package basic

object BasicExample {
def main(args: Array[String]): Unit = {
}
}

6. Set up Apache Spark.

Import the Apache Spark libraries and update your BasicExample.scala file to build and configure a SparkSession.

package basic

import org.apache.spark.SparkConf
import org.apache.spark.sql.{SparkSession}

object BasicExample {
def main(args: Array[String]): Unit = {

val conf = new SparkConf()
.setAppName("BasicExample")
.setMaster("local[*]")

val spark = SparkSession
.builder()
.config(conf)
.getOrCreate()
}
}
  • Lines 3–4: This is where we import the Spark dependencies into our BasicExample.scala class. You must import your dependencies into your class before using them.
  • Lines 9–11: This is where we create our Spark Configuration.
  • Line 10: setAppName() - This specifies the name of your Spark application. This can be whatever you'd like.
  • Line 11: setMaster() - This specifies the URL to your cluster. Since we will be running this locally for demo purposes, we pass in local[*]. The * means to run it with as many worker threads as logical cores on your machine. You can learn more about the master param here.

7. Create sample data files.

Next, create some sample data files in csv format. Later on we'll use Spark to read them into a DataFrame and process them.

In the root of your project, create a new folder called data and three .csv files called users.csv, posts.csv and comments.csv.

Users.csv

id,name,created_at
1,John Doe,2021-01-01
2,Jane Doe,2021-02-01

Posts.csv

id,user_id,title,created_at
1,1,My Sample Post 1,2022-01-01
1,2,My Sample Post 2,2022-03-01

Comments.csv

id,user_id,post_id,text,created_at
1,1,1,How are you doing?,2022-01-04
1,2,1,I am doing well, you?,2022-01-05

Your directory structure should look like this now.

.
├── data
│ ├── comments.csv
│ ├── posts.csv
│ └── users.csv
├── src
│ └── main
│ └── scala
│ └── basic
│ └── BasicExample.scala
└── build.sbt

8. Read CSV files into DataFrames.

Next we’ll create a function within our BaseExample.scala file called readCsv() that can read our csv files into DataFrames.

A DataFrame is an in-memory data set organized into named columns and rows. It is conceptually equivalent to a table in a relational database, but with richer optimizations under the hood.

private def readCsv(
spark: SparkSession,
dataDir: String,
fileName: String
): DataFrame = {
spark.read
.option("header", true)
.csv(s"${dataDir}/${fileName}.csv")
}

Add the above function underneath your main() function.

Your BaseExample.scala file should now look like this:

package basic

import org.apache.spark.SparkConf
import org.apache.spark.sql.{SparkSession, DataFrame}

object BasicExample {
def main(args: Array[String]): Unit = {

val conf = new SparkConf()
.setAppName("BasicExample")
.setMaster("local[*]")

val spark = SparkSession
.builder()
.config(conf)
.getOrCreate()

// todo: ...

}

private def readCsv(
spark: SparkSession,
dataDir: String,
fileName: String
): DataFrame = {
spark.read
.option("header", true)
.csv(s"${dataDir}/${fileName}.csv")
}
}

Next, lets use the newly created readCsv() function to create DataFrames for each of our csv files. Add the following code into your main() function.

// ...

val baseDataPath = sys.env.getOrElse("BASE_DATA_PATH", "./data")

val userDf = readCsv(spark, baseDataPath, "users")
val postDf = readCsv(spark, baseDataPath, "posts")
val commentDf = readCsv(spark, baseDataPath, "comments")

9. Join DataFrames

Now that we have all three files read into a DataFrame, we can perform join logic to create a single output. Add the following into your main function.

// ...

val userDf = readCsv(spark, baseDataPath, "users")
val postDf = readCsv(spark, baseDataPath, "posts")
val commentDf = readCsv(spark, baseDataPath, "comments")

val out = postDf
.join(userDf, postDf("user_id") === userDf("id"))
.join(commentDf, postDf("id") === commentDf("post_id"))
.select(
userDf("id").as("user_id"),
userDf("name"),
postDf("id").as("post_id"),
postDf("created_at").as("post_date"),
commentDf("id").as("comment_id"),
commentDf("created_at").as("comment_date"),
postDf("title"),
commentDf("text")
)
.orderBy("post_date", "comment_date")

Looking at the code above, you can see that we use Sparks join() function to join multiple DataFrame's together. After joining all three DataFrame's together, we use the select() function to only project the columns we need for the final output.

10. Show the outputs.

Finally, we’ll call the .show() function on our final out DataFrame in order to show the results.

// ...

out.show()

The .show() function is a special Spark function that allows developers to review their DataFrames in the console. It will default to only showing you the first 20 rows in the DataFrame, however you can overwrite these limits by passing a numRow parameter into the function like this: .show(1000).

11. Final Code Review

Here’s what your final BasicExample.scala file should look like.

package basic

import org.apache.spark.SparkConf
import org.apache.spark.sql.{SparkSession, DataFrame}

object BasicExample {
def main(args: Array[String]): Unit = {

val conf = new SparkConf()
.setAppName("BasicExample")
.setMaster("local[*]")

val spark = SparkSession
.builder()
.config(conf)
.getOrCreate()

val baseDataPath = sys.env.getOrElse("BASE_DATA_PATH", "./data")

val userDf = readCsv(spark, baseDataPath, "users")
val postDf = readCsv(spark, baseDataPath, "posts")
val commentDf = readCsv(spark, baseDataPath, "comments")

val out = postDf
.join(userDf, postDf("user_id") === userDf("id"))
.join(commentDf, postDf("id") === commentDf("post_id"))
.select(
userDf("id").as("user_id"),
userDf("name"),
postDf("id").as("post_id"),
postDf("created_at").as("post_date"),
commentDf("id").as("comment_id"),
commentDf("created_at").as("comment_date"),
postDf("title"),
commentDf("text")
)
.orderBy("post_date", "comment_date")

out.show()
}

private def readCsv(
spark: SparkSession,
dataDir: String,
fileName: String
): DataFrame = {
spark.read
.option("header", true)
.csv(s"${dataDir}/${fileName}.csv")
}
}

12. Run your code.

Finally, lets run your code and see the results. You first need to open a Terminal session into your root project. If you are using Visual Studio Code, the easiest way is to go to Terminal in the menu and select New Terminal. This should automatically navigate you to your root directory.

In the terminal, enter command sbt to start an SBT session. Then enter run to run your application. You should see the following output in your terminal.

+-------+--------+-------+----------+----------+------------+----------------+------------------+
|user_id| name|post_id| post_date|comment_id|comment_date| title| text|
+-------+--------+-------+----------+----------+------------+----------------+------------------+
| 1|John Doe| 1|2022-01-01| 1| 2022-01-04|My Sample Post 1|How are you doing?|
| 1|John Doe| 1|2022-01-01| 1| 2022-01-05|My Sample Post 1| I am doing well.|
| 2|Jane Doe| 1|2022-03-01| 1| 2022-01-04|My Sample Post 2|How are you doing?|
| 2|Jane Doe| 1|2022-03-01| 1| 2022-01-05|My Sample Post 2| I am doing well.|
+-------+--------+-------+----------+----------+------------+----------------+------------------+

As you can see from the above results, we joined our userDf, postDf and commentDf to create a single DataFrame and printed the results to the console.

Conclusion

We’ve learned how to use sbt to create a Scala based data application using the Apache Spark framework to read csv files into DataFrames, join them up and produce a unified output. Spark's DataFrame API is a powerful tool for data engineering operations.

I highly recommend you continue your research by reading their programming guides and continue your data science/engineering journey.

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Ryan Lindbeck

Strategic Visionary Leader in Healthcare Analytics | Software & Data Engineer