How is this different from List Comparer?

List Comparer reports three sections at once: only-A, only-B, and both. Common List Item Finder is a focused, single-purpose tool that returns only the intersection (both), and errors with a clear message if there's no overlap at all.

How is this different from Distinct List Item Finder?

This tool returns the intersection (shared items). Distinct List Item Finder returns the opposite: the symmetric difference, items in exactly one of the two lists.

What happens if the lists have no items in common?

You'll get an error explaining there's no overlap, rather than a silently empty result.

Common List Item Finder - Find the Intersection of Two Lists

Overview

Introduction

Finding exactly which items two lists share, without the extra only-A/only-B detail, is a focused, common need on its own.

Common List Item Finder returns just that intersection, deduped and in a clean, ready-to-use list.

What Is Common List Item Finder?

A set-intersection tool for two lists: it checks List A's distinct values against List B's set and keeps only the ones present in both.

It's a focused single-purpose alternative to List Comparer's fuller three-section report, when all you need is the overlap.

How Common List Item Finder Works

Both inputs are split into items using the shared selected separator; List B's items are collected into a set for fast membership checks.

List A's distinct values are filtered, keeping only those present in List B's set, in List A's original first-occurrence order.

When To Use Common List Item Finder

Use it to find the overlap between two lists directly, for example shared usernames between two exported member lists.

It's simpler than List Comparer when the only-A and only-B sections aren't relevant to your task.

Often used alongside List Comparer, Distinct List Item Finder and List Subtractor.

Features

Advantages

Focused output: just the intersection, nothing else, deduped and ready to use.
Clear error messaging when there's genuinely no overlap, instead of an ambiguous empty result.

Limitations

Doesn't show what's exclusive to either list; use List Comparer for the full three-section breakdown.
Comparison is exact and case-sensitive with no trimming applied.

Examples

Finding shared items between two lists

Input

List A: a, b, c
List B: b, c, d

Output

b, c

"b" and "c" appear in both lists and are returned; "a" (only in A) and "d" (only in B) are excluded.

No overlap at all

Input

List A: a, b
List B: c, d

Output

(error: no common items)

Since the two lists share nothing, the tool reports a clear error instead of an empty result.

Best Practices & Notes

Best Practices

Use List Comparer instead if you also need to see what's exclusive to each list, not just the shared items.
Chain the result into another list tool, like List Zipper, to pair up the shared values with data from elsewhere.

Developer Notes

Builds a `Set<string>` from List B's items, then filters a deduped `[...new Set(itemsA)]` array against it with `.filter(item => setB.has(item))`, giving each membership check O(1) average time.

Common List Item Finder Use Cases

Finding usernames or IDs shared between two exported membership lists
Checking which tags overlap between two independently curated lists
Verifying data consistency by confirming shared values between two sources

Common Mistakes

Expecting only-A or only-B detail; use List Comparer instead if that context matters.
Assuming List B's own duplicate values change the result; only membership matters, not count.

Tips

If the result is unexpectedly empty, double-check for stray whitespace or casing mismatches between the two lists.
Combine with List Subtractor to also see what's exclusive to List A once you know what's shared.

Common List Item Finder