Quick Answer: What Is FlatMap In Scala?

What is an option in Scala?

Scala Option[ T ] is a container for zero or one element of a given type.

An Option[T] can be either Some[T] or None object, which represents a missing value.

Option type is used frequently in Scala programs and you can compare this with the null value available in Java which indicate no value..

What does a flatMap do?

Description. flatMap() is an intermediate operation and return another stream as method output return value. It returns a stream consisting of the results of replacing each element of the given stream with the contents of a mapped stream produced by applying the provided mapping function to each element.

What is spark RDD in Pyspark?

An Acronym RDD refers to Resilient Distributed Dataset. Basically, RDD is the key abstraction of Apache Spark. In order to do parallel processing on a cluster, these are the elements that run and operate on multiple nodes. Moreover, it is immutable in nature, that says as soon as we create an RDD we cannot change it.

What is difference between MAP and flatMap in Scala?

Both map() and flatMap() are used for transformations. The map() transformation takes in a function and applies it to each element in the RDD and the result of the function is a new value of each element in the resulting RDD. The flatMap() is used to produce multiple output elements for each input element.

What is aggregateByKey spark?

Spark aggregateByKey function aggregates the values of each key, using given combine functions and a neutral “zero value” The aggregateByKey function aggregates values for each key and and returns a different type of value for that key.

What is yield in Scala?

Last Updated: 07-06-2019. yield keyword will returns a result after completing of loop iterations. The for loop used buffer internally to store iterated result and when finishing all iterations it yields the ultimate result from that buffer.

How do you count words in spark?

val text = sc. textFile(“mytextfile.txt”)val counts = text. flatMap(line => line. split.). map(word => (word,1)). reduceByKey(_+_) collect.

What is flatMap in Python?

A flat map is an operation that takes a list which elements have type A and a function f of type A -> [B] . The function f is then applied to each element of the initial list and then all the results are concatenated.

How do you parallelize in spark?

When spark parallelize method is applied on a Collection (with elements), a new distributed data set is created with specified number of partitions and the elements of the collection are copied to the distributed dataset (RDD). First argument is mandatory, while the next two are optional. The method Returns an RDD.

What is spark flatMap?

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.

What is map and flatMap in spark?

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. … While FlatMap() is similar to Map, but FlatMap allows returning 0, 1 or more elements from map function.

Why is RDD reduceByKey better in performance than RDD Groupbykey?

While both reducebykey and groupbykey will produce the same answer, the reduceByKey example works much better on a large dataset. That’s because Spark knows it can combine output with a common key on each partition before shuffling the data.

What is the difference between RDD DataFrame and dataset?

Conceptually, consider DataFrame as an alias for a collection of generic objects Dataset[Row], where a Row is a generic untyped JVM object. Dataset, by contrast, is a collection of strongly-typed JVM objects, dictated by a case class you define in Scala or a class in Java.

What is spark mapValues?

mapValues is only applicable for PairRDDs, meaning RDDs of the form RDD[(A, B)]. In that case, mapValues operates on the value only (the second part of the tuple), while map operates on the entire record (tuple of key and value).

How do you write a loop in Scala?

In Scala, for-loop allows you to filter some elements from the given collection using one or more if statements in for-loop. Syntax: for(i<- List if condition1; if condition2; if condition3; ...) { // code.. }

What is reduce in spark?

reduce(func) Reduce is a spark action that aggregates a data set (RDD) element using a function. That function takes two arguments and returns one. The function must be parallel enabled. reduce can return a single value such as an int.

What is Scala list?

A list is a collection which contains immutable data. … The Scala List class holds a sequenced, linear list of items. Following are the point of difference between lists and array in Scala: Lists are immutable whereas arrays are mutable in Scala. Lists represents a linked list whereas arrays are flat.

What is for comprehension in Scala?

Scala’s “for comprehensions” are syntactic sugar for composition of multiple operations with foreach , map , flatMap , filter or withFilter . Scala actually translates a for-expression into calls to those methods, so any class providing them, or a subset of them, can be used with for comprehensions.