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https://issues.apache.org/jira/browse/NIFI-15628?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18061032#comment-18061032
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ASF subversion and git services commented on NIFI-15628:
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Commit efb54cb39ffca8347ca5d79076dcbfc62a0a93ad in nifi's branch
refs/heads/main from mcducks
[ https://gitbox.apache.org/repos/asf?p=nifi.git;h=efb54cb39f ]
NIFI-15628 - Add unique() expression language function
- Added UniqueEvaluator for removing duplicates from delimited strings
- Preserves order of first occurrence using LinkedHashSet
- Handles special regex characters with Pattern.quote()
- Empty strings treated as distinct values
- Added unit tests
- Updated ANTLR grammar (lexer and parser)
- Integrated into ExpressionCompiler with proper type coercion
- Added documentation to expression language guide
This closes #10923.
Signed-off-by: Pierre Villard <[email protected]>
> 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
> Priority: Minor
> Fix For: 2.9.0
>
> Time Spent: 1.5h
> Remaining Estimate: 0h
>
> 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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