Working with large volumes of document data for analytics requires the power and flexibility of MongoDB's Map-reduce feature. In this course, Querying Data Using Map-reduce in MongoDB, you'll gain the ability to get yourself fully equipped to confidently apply the Map-reduce pattern to any data set no matter how large it could be. First, you'll discover the requirement for Map-reduce among other aggregation capabilities of MongoDB. Next, you'll explore how to create a custom jаvascript map function and a reduce function that are needed to perform map and reduce operations. Finally, you'll learn how to use these custom functions to perform a Map-reduce operation on a MongoDB data set to aggregate results across documents. When you're finished with this course, you'll have the skills and knowledge of working with the Map-reduce function in MongoDB that will help you leverage the power of MongoDB's aggregation feature for data crunching requirements in your next project.