> For the complete documentation index, see [llms.txt](https://docs.dataspace.ch/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.dataspace.ch/platform/transformation/preview.md).
# Preview
The preview panel allows previewing the data (max 200 rows), sorting by column, and performing filters.
Once a Transformation has been successfully built, the data is stored in a `.parquet` file and can be efficiently queried and previewed.
By clicking on the details button next to the column names, a statistics panel will open up, giving an overview and some metadata about said column, such as:
* Distinct Count
* Null Count
* Min/Max values
The panel also shows a breakdown of unique values and their frequency and gives the possibility to search by value.
### Custom Filter
The filter input at the top of the preview panel allows SQL-style `WHERE` clause to be applied.
Following is an example filter:
```
"Airline" = 'Air France' AND "To" = 'JFK'
```
### Data Extract
The generated dataset can be extracted as a CSV or Parquet file using the export buttons at the bottom of the table.
{% hint style="info" %}
Please note that the [EXPORTER](file:///5959076/user-roles.md#exporter) role is required to be able to extract data
{% endhint %}
---
# Agent Instructions
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## 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.dataspace.ch/platform/transformation/preview.md?ask=&goal=
```
`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.
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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.