When having a field containing for instance campaign codes it is often better to replace these with more readable variants. This can be done with Funnel rules either using the conventional "WHEN condition THEN value" or Inline Lookup Tables.

Maintaining these rules can be cumbersome especially when there are frequent changes to the lookup values.

To make this easier, you can connect a Google Sheet, with the lookup values, as a source in Funnel and create a new "Custom Dimension" from the "Dimensions" page in Funnel.

Add a rule for all data, select the field to use for the lookup ("Campaign" in this example), and click "+ more steps".

Select "lookup", and change the source of the lookup from "Comma-separated values" to the Google Sheet that contains your lookup values:

Select which field to look for in "IN FIELD" and which field to return in "RETURN", for instance "Campaign code" and "Campaign name".

Matching can be fine-tuned by changing comparison operator in "MATCH USING".

The sheet may only contain up to 5000 rows.
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For a 'Funnel Dimension', both columns in the google sheet must contain string values and for a 'Metric' both columns must contain numeric values.