> For the complete documentation index, see [llms.txt](https://1spatial.gitbook.io/fme-form-beginner/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://1spatial.gitbook.io/fme-form-beginner/transformer-usage/conditional-filtering.md).
# Conditional Filtering
Transformers that filter, don’t transform data content, yet surveys show that they’re the most commonly used type of transformer there is!
## What is Filtering?
Filtering is the technique of subdividing data as it flows through a workspace. It’s the case where there are multiple output connections from a transformer, each of which carries data to be processed differently. Here (for example) incoming stream A is filtered into two new streams, B and C:
A filtering transformer may be any transformer with multiple output ports, such as the GeometryFilter or Sampler transformers, the latter of which creates a sample selection of data and separates it out through Sampled and NotSampled output ports:
However, these are mostly in-built, fixed tests. Conditional filtering is where the decision about which features are output to which connection is decided by some form of user-defined test or condition. The Tester transformer is the most obvious example of this. It carries out a test and has different output ports for features that pass and fail the test.
---
# 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:
```
GET https://1spatial.gitbook.io/fme-form-beginner/transformer-usage/conditional-filtering.md?ask=
```
The question should be specific, self-contained, and written in natural language.
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.