Java: Data Science Made Easy

Hadoop MapReduce

As we already said, Hadoop MapReduce is a library, that allows you to process data in a scalable way. 

There are two main abstractions in the MapReduce framework: Map and Reduce. This idea originally comes from the functional programming paradigm, where map and reduce are high-level functions:

• map: This takes in a function and a sequence of elements and applies the function to each of the elements in turn. The result is a new sequence. 
• reduce: This also takes in a function and a sequence, and it uses this function to process the sequence and ultimately return a single element in the end. 

In this book, we have already used the map function from the Java Stream API quite extensively, starting with Chapter 2, Data Processing ...