Documents grouping

One of the most desired functionalities in Elasticsearch was always a feature called document folding or document grouping. This functionality was the most +1 marked issue for Elasticsearch. It is not surprising at all. It is sometimes very convenient to show a list of documents grouped by a particular value, especially when the number of results is very big. In this case, instead of showing all the documents one by one, we would return only one (or a few) documents from every group. For example, in our library, we could prepare a query returning all the documents about wildlife sorted by publishing date, but limit the list to two books from every year. The other useful use case, where grouping can become very handy, is counting ...

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