Collectors: Grouping Operations
Explore the grouping operations available in Java 8 Stream API's Collectors class. Learn how to group data by custom keys, perform downstream aggregations like sum and max, and partition data with predicates. This lesson helps you simplify complex data grouping tasks into concise, readable code using groupingBy and partitioningBy collectors.
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Grouping operations
Grouping operations are one of the most important features of streams because they can help you complete a task, which otherwise would have taken a lot of coding, in just 2-3 lines of code.
Let’s say, for example, we have a list of Employee objects. We need to group all our employees based on their countries of residence.
Or, say we need to find the average age/salary of all employees in a particular country.
These kinds of operations can be done very easily with grouping APIs provided in the Collectors class.
Let’s explore these APIs in detail.
1) Collectors.groupingBy()
This method groups the input elements according to the supplied classifier and returns the results in a Map.
This method is similar to ...