Chapter 7: Aggregations

In developing search solutions, not only are the results important, but they also help us to improve the quality and the search focus. Elasticsearch provides a powerful tool to achieve these goals: aggregations. The main usage of aggregations is to provide additional data to the search results to improve their quality or to augment them with additional information.

For example, in a search for news articles, some facets that could be interesting to calculate could be the authors who wrote the articles and the date histogram of the publishing date; thus, aggregations are used, not only to improve the results' focus, but also to provide insight into stored data (analytics). This is the way that a lot of tools such as Kibana (https://www.elastic.co/products/kibana) are born.

Generally, aggregations are displayed to the end user with graphs or a group of filtering options (for example, a list of categories for the search results). Because the Elasticsearch...