Apache Spark Map vs FlatMap Operation

1. Objective

In this Apache Spark tutorial, we will discuss the comparison between Spark Map vs FlatMap Operation. Map and FlatMap are the transformation operations in Spark. Map() operation applies to each element of RDD and it returns the result as new RDD. In the Map, operation developer can define his own custom business logic. While FlatMap() is similar to Map, but FlatMap allows returning 0, 1 or more elements from map function.

In this blog, we will discuss how to perform map operation on RDD and how to process data using FlatMap operation. This tutorial also covers what is map operation, what is a flatMap operation, the difference between map() and flatMap() transformation in Apache Spark with examples. We will also see Spark map and flatMap example in Scala and Java in this Spark tutorial.

So, let’s start Spark Map vs FlatMap function.

Apache Spark Map vs FlatMap Operation

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2. Difference between Spark Map vs FlatMap Operation

This section of the Spark tutorial provides the details of Map vs FlatMap operation in Apache Spark with examples in Scala and Java programming languages.

i. Spark Map Transformation

A map is a transformation operation in Apache Spark. It applies to each element of RDD and it returns the result as new RDD. In the Map, operation developer can define his own custom business logic. The same logic will be applied to all the elements of RDD.

Spark Map function takes one element as input process it according to custom code (specified by the developer) and returns one element at a time. Map transforms an RDD of length N into another RDD of length N. The input and output RDDs will typically have the same number of records.

Apache Spark map transformation operation

a. Map Transformation Scala Example

Create RDD

val data = spark.read.textFile("INPUT-PATH").rdd

Above statement will create an RDD with name data. Follow this guide to learn more ways to create RDDs in Apache Spark.

Map Transformation-1

val newData = data.map (line => line.toUpperCase() )

Above the map, a transformation will convert each and every record of RDD to upper case.

Map Transformation-2

val tag = data.map {line => {
val xml = XML.loadString(line)
xml.attribute("Tags").get.toString()
}
}

Above the map, a transformation will parse XML and collect Tag attribute from the XML data. Overall the map operation is converting XML into a structured format.

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b. Map Transformation Java Example

Create RDD

JavaRDD<String> linesRDD = spark.read().textFile("INPUT-PATH").javaRDD();

Above statement will create an RDD with name lines RDD.

Map Transformation

JavaRDD<String> newData = linesRDD.map(new Function<String, String>() {
public String call(String s) {
String result = s.trim().toUpperCase();
return result;
}
});

We recommend you to read – Spark Shell Commands to Interact with Spark-Scala

ii. Spark FlatMap Transformation Operation

Let’s now discuss flatMap() operation in Apache Spark-

Apache Spark flatMap transformation operation

A flatMap is a transformation operation. It applies to each element of RDD and it returns the result as new RDD. It is similar to Map, but FlatMap allows returning 0, 1 or more elements from map function. In the FlatMap operation, a developer can define his own custom business logic. The same logic will be applied to all the elements of the RDD.

A FlatMap function takes one element as input process it according to custom code (specified by the developer) and returns 0 or more element at a time. flatMap() transforms an RDD of length N into another RDD of length M.

a. FlatMap Transformation Scala Example

val result = data.flatMap (line => line.split(" ") )

Above flatMap transformation will convert a line into words. One word will be an individual element of the newly created RDD.

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b. FlatMap Transformation Java Example

JavaRDD<String> result = data.flatMap(new FlatMapFunction<String, String>() {
public Iterator<String> call(String s) {
return Arrays.asList(s.split(" ")).iterator();
} });

Above flatMap transformation will convert a line into words. One word will be an individual element of the newly created RDD.

3. Conclusion

Hence, from the comparison between Spark map() vs flatMap(), it is clear that Spark map function expresses a one-to-one transformation. It transforms each element of a collection into one element of the resulting collection. While Spark flatMap function expresses a one-to-many transformation. It transforms each element to 0 or more elements.

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See Also-

• Apache Spark compatibility with Hadoop

Reference for Spark