What is a Regex Filter? Examples and Use Cases

Regex filter

Pattern-based rules for including or excluding analytics data using regular expressions.

Definition and Key Concepts

• Regular expression (regex)

  A sequence of characters that defines a search pattern. In analytics, regex is used to match parts of strings like URLs, event names, or user agents.

  • Metacharacters:

    Symbols like . (any character), * (zero or more), and + (one or more) that control matching behavior.

  • Character classes:

    Sets of characters in brackets, e.g., [A-Za-z0-9], define allowed matches.

  • Anchors:

    ^ and $ assert the start and end of a string, ensuring precise matches.

• Regex filter in analytics

  A mechanism that applies regex patterns to incoming analytics data to include or exclude data points based on match results.

  • Inclusion filters:

    Keep only data that matches a given pattern, e.g., include URLs starting with /blog using ^/blog.

  • Exclusion filters:

    Remove data matching the pattern, such as excluding internal IP ranges.

  • Processing order:

    Filters are evaluated in the order defined, so the sequence can affect results.

Implementing Regex Filters in GA4

• Create a custom data filter

  In GA4 Admin, navigate to Data Settings > Data Filters to build a custom filter that uses regex conditions.

  • Access the admin ui:

    Go to Admin > Data Settings > Data Filters in your GA4 property.

  • Add new filter:

    Click Create Filter, select Custom, and name your filter.

  • Define regex condition:

    Set the field (e.g., Event name), choose matches regex, and enter your pattern (e.g., ^video_).

  • Save and publish:

    Review with the Preview option, then Publish to activate the filter.

• Validate and debug filters

  Ensure your regex patterns work as expected using GA4’s DebugView and real-time reports.

  • Use debugview:

    Send test events from your site or Measurement Protocol to see matching behavior live.

  • Monitor realtime reports:

    Check if events appear or disappear according to your filter.

  • Review filter status:

    In Data Filters, inspect the filter’s status and hit counts.

Implementing Regex Filters in Plainsignal

• Configure filters via window.psconfig

  Before loading the PlainSignal script, define window.psConfig.filters with regex filter objects.

  • Filter object structure:

    { type: 'exclude', field: 'url', match: 'regex', pattern: '^/admin' }

  • Available fields:

    url, referrer, userAgent

  • Filter types:

    include to keep matches, exclude to drop them.

• Example: excluding internal paths

  <script>
    window.psConfig = {
      filters: [{ type: 'exclude', field: 'url', match: 'regex', pattern: '^/internal' }]
    };
  </script>
  <link rel='preconnect' href='//eu.plainsignal.com/' crossorigin/>
  <script defer data-do='yourwebsitedomain.com' data-id='0GQV1xmtzQQ' data-api='//eu.plainsignal.com' src='//cdn.plainsignal.com/PlainSignal-min.js'></script>
  

  • Pattern:

    ^/internal matches all paths starting with /internal.

  • Type:

    exclude drops matching hits.

  • Position:

    Place the config before the PlainSignal script tag.

Best Practices and Troubleshooting

• Keep patterns specific

  Use anchors and character classes to avoid unintended matches.

  • Use anchors:

    Start (^) and end ($) anchors limit matches.

  • Escape special characters:

    Prefix metacharacters like . or * with backslash (e.g., \.) when matching literally.

• Test regularly

  Validate patterns in regex testers or platform previews before applying.

  • Online tools:

    Use sites like regex101.com for real-time feedback.

  • Platform previews:

    GA4 offers a Preview option for Data Filters.

• Monitor impact

  Review your reports after filter changes to ensure accuracy.

  • Compare time periods:

    Look for sudden drops or spikes after filter activation.

  • Use developer mode:

    Open DebugView or browser console to confirm filtering behavior.

Related terms