Richard Scott created NIFI-15628:
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Summary: Add Expression Language function unique(delimiter) to
return unique delimited values
Key: NIFI-15628
URL: https://issues.apache.org/jira/browse/NIFI-15628
Project: Apache NiFi
Issue Type: Improvement
Components: NiFi API
Reporter: Richard Scott
This function returns the *unique values* from a {*}delimited string{*},
{*}preserving the order of first occurrence{*}. The function takes a delimiter
argument, splits the subject string on that delimiter, removes duplicate tokens
while keeping the first occurrence, and joins the remaining tokens using the
same delimiter.
*Subject Type:* String
*Arguments:*
* {{delimiter}} (String): delimiter used to split and join the subject string
*Return Type:* String
h2. Use Case
Many flows produce list-like attributes (e.g., tags, labels, realms, paths,
routing hops) that accumulate duplicates as processing continues. A built-in
function to deduplicate while preserving the original order improves
readability, consistency, and downstream matching without requiring scripting.
h2. Examples
If the {{tags}} attribute has value:
{{red,blue,red,green,blue,yellow}}
||Expression||Value||
|{{{}$\{tags:unique(','){}}}}|{{red,blue,green,yellow}}|
|{{{}$\{tags:unique(';'){}}}}|{{red,blue,red,green,blue,yellow}}|
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