Aggregation:

 Aggregation in MongoDB refers to the process of performing data transformation operations on a collection, such as grouping, filtering, sorting, and computing aggregate values.


 It allows you to process and analyze data from multiple documents within a collection to derive meaningful insights.


MongoDB provides the Aggregation Framework, which is a powerful set of operators and stages for performing complex data aggregations.


 The Aggregation Framework operates on the concept of pipelines, where a series of stages are applied sequentially to transform the input data and produce the desired results.


Each stage in an aggregation pipeline takes the output of the previous stage as its input and performs a specific operation. Some commonly used stages in the Aggregation Framework include:


$match: Filters the documents based on specified conditions to select a subset of data for further processing.


$group: Groups the documents based on specified criteria and performs calculations or transformations on the grouped data using aggregation operators.


$project: Specifies which fields to include or exclude from the output documents and allows you to reshape the structure of the documents.

$addFields: Adds new fields to documents with specified values or computed expressions.

$expr: Allows the use of aggregation expressions within other operators or stages to perform complex logical and comparison operations.


$sort: Sorts the documents based on specified criteria.


$limit: Restricts the number of documents in the output to a specified limit.


$skip: Skips a specified number of documents in the input and passes the remaining documents to the next stage.


$lookup: Performs a left outer join between two collections to retrieve matching documents from a secondary collection.


$unwind: Deconstructs an array field from the input documents and outputs a document for each element of the array.


$addFields: Adds new fields to documents with specified values or computed expressions.

$expr: Allows the use of aggregation expressions within other operators or stages to perform complex logical and comparison operations.


$sum, $avg, $min, $max: Aggregation operators that perform calculations on numeric values within a group.


By combining these stages in various ways, you can create complex aggregation pipelines to manipulate and analyze your data. Aggregation in MongoDB is particularly useful for tasks such as generating reports, calculating statistics, and summarizing large datasets.


The Aggregation Framework is flexible, efficient, and well-suited for handling large volumes of data. It provides a robust set of tools for data analysis and enables you to perform complex transformations on your data directly within the MongoDB database.