How is this different from List Comparer?

List Comparer handles exactly two lists, reporting only-A, only-B, and both. Three-List Comparer extends this to three input lists, reporting items in all three, items in exactly two of the three (regardless of which pair), and items unique to exactly one list.

Does it tell me which specific two lists share an "exactly two" item?

No, the "exactly two" section reports the value only, not which pair of lists it came from. If you need that detail, run List Comparer pairwise on each combination of two of your three lists.

What happens if one of the three lists is empty?

You'll get an error naming which list is empty, since a meaningful three-way comparison requires all three lists to have content.

Three-List Comparer - Compare Three Lists at Once

Overview

Introduction

Comparing three related lists at once, for example three different exports of the same dataset, quickly becomes hard to reason about with only pairwise comparison tools.

Three-List Comparer classifies every value across all three lists in one pass by how many of the three lists it appears in.

What Is Three-List Comparer?

A three-list set comparison tool: it computes, for every distinct value across all three lists, whether it appears in all three, exactly two, or exactly one.

It's the natural three-way generalization of List Comparer, replacing three separate pairwise comparisons with a single combined report.

How Three-List Comparer Works

All three inputs are split into items using the shared selected separator, each forming a set of distinct values.

Every distinct value across the union of all three sets is classified by counting how many of the three sets contain it, then grouped into the all-three, exactly-two, and unique-to-one sections.

When To Use Three-List Comparer

Use it to find values consistent across three data sources versus values that only partially agree.

It's useful for reconciling three versions of a list, for example three team members' independently compiled tag lists.

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

Features

Advantages

Classifies every value's membership across all three lists in a single pass, instead of three separate pairwise comparisons.
Preserves first-seen order across the combined lists within each output section.

Limitations

The "exactly two" section doesn't identify which specific pair of lists shares each value.
Comparison is exact and case-sensitive with no trimming applied.

Examples

Three overlapping lists

Input

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

Output

In all three: c
In exactly two: b, d
Unique to one: a, e

"c" appears in all three lists, "b" and "d" each appear in exactly two, and "a"/"e" each appear in only one list.

No values shared by all three

Input

List A: x, y
List B: y, z
List C: z, w

Output

In exactly two: y, z
Unique to one: x, w

No value appears in all three lists, so the "in all three" section is empty while the other two sections still populate normally.

Best Practices & Notes

Best Practices

Use List Comparer instead when you only have two lists, since its two-section-plus-both output is simpler to read.
Follow up with a pairwise List Comparer run if you need to know exactly which two lists share an "exactly two" value.

Developer Notes

Builds three `Set<string>` objects and a combined first-seen-order array from all three inputs' items, then classifies each distinct value by summing three `.has()` boolean checks (`setA.has(x) + setB.has(x) + setC.has(x)` conceptually) into a 1, 2, or 3 count.

Three-List Comparer Use Cases

Reconciling three independently compiled versions of the same list
Finding values that only partially agree across three data exports
Auditing consistency across three related datasets in one pass

Common Mistakes

Expecting to see which specific pair of lists an "exactly two" value came from; that detail isn't broken out.
Forgetting all three lists share one separator setting.

Tips

If a value is missing from the "in all three" section unexpectedly, check for stray whitespace or casing differences across your three lists.
Chain the "in all three" section into another list tool once you've confirmed full agreement.

Three-List Comparer