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Learn how to effectively sort buckets in Elasticsearch Terms aggregation by the length of string keys for more relevant results.
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Sorting Results of Elasticsearch Terms Aggregation by Key String Length

When working with Elasticsearch, you may often need to perform aggregations to retrieve unique values from a particular field. One common scenario is when you want to find the first N unique values of a string field, but sorted in a way that is most relevant to your search criteria. In this guide, we will explore how to sort the results of a Terms aggregation by the length of the string keys, which can yield more useful results compared to a mere alphabetical sorting.

The Problem

You’re querying Elasticsearch with a Terms aggregation and want to extract unique values of a string field, foo, which includes a specific substring, bar. Your current approach allows you to sort the results alphabetically, but you find that shorter strings are more relevant to your search and should appear first in your results.

Current Query Structure

Here is an example of how your current query might look:

[[See Video to Reveal this Text or Code Snippet]]

Example Output

When you run the above query, the output looks like this:

[[See Video to Reveal this Text or Code Snippet]]

The issue here is that the results are sorted alphabetically, rather than by the length of the strings in the foo field.

The Solution

To achieve the desired result of sorting by string length, we need to implement a sub-aggregation in our query that calculates the length of each string key. We can then order the outer aggregation by this newly calculated length and alphabetically by the key itself.

Updated Query Structure

Here is how you can modify your query:

[[See Video to Reveal this Text or Code Snippet]]

Explanation of Changes

Sub-Aggregation (key_length): This sub-aggregation uses a script to calculate the length of each string in the foo field.

Ordering: The order now specifies that results should be sorted first by key_length (ascending), and then by _key (ascending) for strings of the same length.

Expected Output

With this modification, you should get results similar to the following:

[[See Video to Reveal this Text or Code Snippet]]

In this new output, shorter strings appear first, proving that they are considered a better match based on your substring criteria.

Conclusion

Sorting results based on string lengths in Elasticsearch can significantly improve the relevance of the data returned from your queries. By utilizing sub-aggregations, you have the flexibility to craft more intricate sorting mechanisms that can enhance your data retrieval strategies. Implement the above changes into your Elasticsearch queries to sort by key string lengths and enjoy better results!