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find-unique-items

Finding unique items means returning the items that appear exactly once in the input — the opposite of finding duplicates. If a list has 1000 entries and 950 are duplicates of something, "unique items" returns the 50 singletons. This is different from deduplication, which keeps one of every distinct value. Use cases: spotting one-time events in a log, isolating outliers in a dataset, finding rare values for analysis. The ZTools Find Unique Items tool counts occurrences in O(n) using a hash map and returns only items with count = 1.

Use cases​

Identify rare events in logs​

Most error codes repeat thousands of times. The unique ones — codes that fired exactly once — are often the most interesting (one-off bugs, edge cases).

Find one-time customers​

In a transaction list, customers appearing only once might churn. Surface them for re-engagement campaigns.

Spot outliers in survey responses​

Most write-ins repeat common answers. The unique write-ins are the ones to read — they're where insight lives.

Audit a migration​

After a CSV import, the IDs that appear in the source but not the destination (and vice versa) tell you what failed.

How it works​

  1. Paste list — One item per line. Tool counts occurrences in a hash map (Map in JS).
  2. Filter to count = 1 — Walk the map, keep only items with frequency = 1. Output the keys preserving original order.
  3. Configure matching — Case-sensitive / insensitive, whitespace trim, numeric coercion. Same options as dedupe.
  4. Copy result — Output uniques + count summary: {input: 1000, distinct: 425, unique once: 50}.

Examples​

Input: [apple, banana, apple, cherry, banana, date]

Output: Unique items: [cherry, date]. Each appears exactly once.

Input: Logs with 10,000 lines and 9,800 duplicates

Output: Unique items: 200 lines that fired only once. Often the most informative.

Input: Case-insensitive: ["Alice","alice","Bob"]

Output: With case-insensitive: alice appears 2x, Bob 1x → unique: [Bob]. Without: all three are distinct strings, all appear once → unique: all three.

Frequently asked questions​

How is this different from dedupe?

Dedupe returns one of each distinct value (apple appears 3x → output keeps one apple). Unique returns only items with frequency 1 (apple appears 3x → output drops apple entirely).

What does "find unique" mean exactly?

Items with count exactly 1. Items with count 0 don't exist; items with count ≥ 2 are duplicates and excluded.

Can I see the full frequency table?

Toggle "show frequencies" — output becomes a table of (item, count) pairs sorted by count. Useful for triage.

How big a list?

O(n) hash-map walk. Million-line inputs work in seconds.

Privacy?

All client-side. No upload.

Tips​

  • Combine with sort to produce a sorted list of uniques — easier scanning.
  • Toggle case-insensitive when working with names or emails — "Alice" and "alice" should usually be one entity.
  • For the inverse (only items that repeat), use the Find Duplicate Items tool.
  • Frequency view is the secret weapon — a table of (item, count) sorted descending tells you both the most-common and the rarest items at a glance.

Try it now​

The full find-unique-items runs in your browser at https://ztools.zaions.com/find-unique-items — no signup, no upload, no data leaves your device.

Open the tool ↗

Last updated: 2026-05-06 · Author: Ahsan Mahmood · Edit this page on GitHub