Duplicate List Item Finder

Scans a separator-delimited list and outputs every duplicate occurrence beyond the first, that is, every "extra" copy of a repeated value, in original order. For ["a", "b", "a", "a"] the output is "a\na" (the 2nd and 3rd copies), never the first "a" that established the value. A free online tool from Staaarter, right in your browser.

Runs locallyUpdated 2026-07-27

Overview

Introduction

Sometimes you need to see the actual extra copies of a duplicated value, not just a tally, for example to manually inspect or delete each redundant row.

Duplicate List Item Finder lists every occurrence of a value after its first appearance, preserving the list's original order.

What Is Duplicate List Item Finder?

A duplicate-occurrence extractor: as it walks the list, the first time it sees a value it remembers it; every subsequent time that same value appears, that occurrence is reported as a duplicate.

The output is a real list of raw duplicate items (not annotated with counts), so it can be fed directly into other list tools.

How Duplicate List Item Finder Works

The input is split into items using the selected separator, then walked in order while tracking which values have already been seen.

Any item matching a value already seen is added to the output; the first occurrence of every value is skipped since it isn't itself a duplicate.

When To Use Duplicate List Item Finder

Use it when you need the actual extra rows, not a summary count, for example to review or manually delete redundant entries one by one.

It's useful upstream of List Item Deleter, once you know exactly which raw values are duplicated.

Features

Advantages

  • Preserves every individual duplicate occurrence in original order, not a collapsed summary.
  • Output is a plain list, directly chainable into other list tools.

Limitations

  • Doesn't show counts per value; use Repeating List Item Finder for that summary view.
  • Comparison is exact and case-sensitive with no trimming applied.

Examples

Worked example: extra copies only

Input

a
b
a
a

Output

a
a

The list has three "a" values. The first "a" establishes the value and is excluded; the 2nd and 3rd "a" occurrences are the extras and are listed.

Comparing to Repeating List Item Finder's output

Input

apple
banana
apple
apple

Output

apple
apple

Repeating List Item Finder would output "apple (×3)" for this same input; this tool instead lists the two extra "apple" occurrences individually.

Best Practices & Notes

Best Practices

  • Use this tool when you plan to review or act on each duplicate row individually; use Repeating List Item Finder for a summary count instead.
  • Combine with Repeating List Item Remover to see the before (all extras) and after (deduped list) views side by side.

Developer Notes

Walks the split array once, tracking seen values in a `Set<string>`; an item is pushed to the extras array only when `seen.has(item)` is already true, otherwise it's added to `seen` as the establishing occurrence.

Duplicate List Item Finder Use Cases

  • Reviewing every redundant row in a pasted dataset before deciding how to handle each one
  • Auditing a list for accidental copy-paste duplication
  • Feeding extra duplicate rows into another tool for further processing

Common Mistakes

  • Expecting the first occurrence of a repeated value to appear in the output; by design it never does.
  • Confusing this with Repeating List Item Finder's collapsed count-per-value output.

Tips

  • If the output is longer than expected, remember every extra copy is listed individually, so a value repeating five times contributes four lines.
  • Run Repeating List Item Remover afterward to get a fully de-duplicated list.

References

Frequently Asked Questions