> For the complete documentation index, see [llms.txt](https://docs.fractalworks.io/joule/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.fractalworks.io/joule/components/pipelines/group-by.md).

# Group by

## Overview

To effectively implement window-based aggregate analytics in streaming applications, the `GROUP BY` clause is essential. Many streaming architectures utilise time windows to analyse data, whether defined by a specific time interval or a fixed number of events.

For instance, to determine the average bid price for each market symbol, we can group events by the symbol and compute the average within each time window. This approach not only condenses the volume of events published by the system but also enhances overall processing efficiency. 

By leveraging the `GROUP BY` functionality, we can optimise resource usage while maintaining the integrity of real-time analytics.

{% hint style="warning" %}
group by is required and must be provided with at least one valid attribute
{% endhint %}

## Example

In the following example we are grouping events by market and then by symbol. 

```yaml
stream:
  ...
  group by:
    - market
    - symbol
```


---

# Agent Instructions
This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com.

## Querying This Documentation
If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter, and the optional `goal` query parameter:

```
GET https://docs.fractalworks.io/joule/components/pipelines/group-by.md?ask=<question>&goal=<endgoal>
```

`ask` is the immediate question: it should be specific, self-contained, and written in natural language.
`goal` is optional and describes the broader end goal you are ultimately trying to accomplish on behalf of the user. GitBook uses it to tailor the answer towards what is most useful for that goal.

The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.