fix(intersectionBy): remove duplicates when mapper produces same values

[wo-o29]

Summary

Fixes: #956

Fixed a bug in intersectionBy where it returned duplicate elements from the first array when the mapper function produced identical values for multiple elements. Now correctly returns only the first occurrence of each mapped value.

For example, intersectionBy([2.1, 2.2], [2.3, 3.4], Math.floor) now correctly returns [2.1] instead of [2.1, 2.2].

Changes

• Modified intersectionBy to use uniqBy on the first array before filtering
• Added test case to verify duplicate removal behavior

Comment

• Would it be better to implement it myself rather than using the uniqBy function?

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Project	Deployment	Preview	Comments	Updated (UTC)
es-toolkit	Ready	Preview	Comment	Nov 24, 2025 3:00am

[Copilot]

Pull Request Overview

This PR enhances the intersectionBy function to support finding the intersection of three or more arrays using a mapping function, while maintaining backward compatibility with the existing two-array signature. The enhancement allows developers to find common elements across multiple arrays based on a transformed value, which is useful for complex data filtering scenarios.

Key Changes:

• Modified the function signature to accept a variable number of arrays using rest parameters, with the mapper function as the last argument
• Updated implementation to iteratively filter elements across all provided arrays
• Added comprehensive test coverage for 3+ array scenarios and edge cases

Reviewed Changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 7 comments.

Show a summary per file

File	Description
src/array/intersectionBy.ts	Enhanced function to support multiple arrays with iterative filtering logic and updated JSDoc documentation
src/array/intersectionBy.spec.ts	Added test cases for 3+ arrays, 4+ arrays, and empty intersection scenarios
docs/reference/array/intersectionBy.md	Updated English documentation with multi-array examples and parameter descriptions
docs/ko/reference/array/intersectionBy.md	Updated Korean documentation with multi-array examples and parameter descriptions
docs/ja/reference/array/intersectionBy.md	Updated Japanese documentation with multi-array examples and parameter descriptions
docs/zh_hans/reference/array/intersectionBy.md	Updated Chinese documentation with multi-array examples and parameter descriptions

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[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.97%. Comparing base (b6ffb6d) to head (2475241).
⚠️ Report is 5 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1528   +/-   ##
=======================================
  Coverage   99.97%   99.97%           
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  Files         474      474           
  Lines        4492     4493    +1     
  Branches     1313     1313           
=======================================
+ Hits         4491     4492    +1     
  Misses          1        1           

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[raon0211]

I'm sorry, but as we mentioned in the original comment, we would like to keep the original interface where we only accept two arrays and a mapper function. (We would not like to accept multiple arrays here since it violates our simplicity principle.)

However, we should fix a bug where calls like intersectionBy([2.1, 2.2], [2.3, 3.4], Math.floor) does not return [2.1]. (It is returning [2.1, 2.2].)

[wo-o29]

Sorry, I seem to have misunderstood your comment. I'll try to fix the bug you mentioned by submitting a PR.

[wo-o29]

@raon0211

I've fixed the bug and re-created the PR, sorry for the confusion.