Text Deduplication Tool
Quickly remove duplicate content from text, supporting line, word, sentence, and paragraph deduplication
What is Text Deduplication?
Text Deduplicate removes repeated lines, words, or entries from a text so lists become cleaner and easier to review. It helps clean imported CSV snippets, keyword lists, email collections, log fragments, product codes, prompt variants, and notes where duplicates appeared through copying, merging, or broken exports. The important part is the comparison rule: case sensitivity, leading or trailing spaces, blank lines, punctuation, normalization, and original order can all determine whether two entries should be treated as the same. The tool speeds up cleanup, but it does not replace domain review when similar entries must remain separate or small differences carry meaning.
How to Use
Basic Operations
- Enter or paste the text to deduplicate in the left text box
- Select the appropriate deduplication mode (by line, word, sentence, etc.)
- Adjust options as needed (case sensitivity, keep order, etc.)
- View real-time deduplication results and statistics on the right
- Click the copy button to save results to clipboard
Mode Description
- By Line: Treats each line as an independent unit, removes identical lines
- By Word: Splits text by spaces, removes duplicate words
- By Sentence: Splits by periods, question marks, exclamation marks, removes duplicate sentences
- By Paragraph: Splits by blank lines, removes duplicate paragraphs
- By Character: Removes characters that appear multiple times in text
Use Cases
Technical Principle
Deduplication is a one-pass scan backed by a JavaScript Set. ECMAScript Set uses the SameValueZero equality algorithm (the same comparison Array.prototype.includes uses, where NaN equals NaN but +0 equals -0) and is required by the spec to deliver sublinear average lookup — V8 implements it as an open-addressing hash table with O(1) amortized insert and has, so the whole pass is O(n) in the number of items. The naive alternative — pushing into a result array and calling indexOf on every element — is O(n²) and becomes painful around 10k entries. Splitting is mode-specific: line mode splits on /\r?\n/ to absorb both CRLF (Windows) and LF (Unix) line endings, word mode splits on /\s+/, sentence mode splits on /(?<=[.!?])\s+/, and paragraph mode splits on /\n{2,}/. Each unit is run through optional normalizers before it becomes a Set key: trim() to strip leading and trailing whitespace, toLowerCase() for case-insensitive matching, and String.prototype.normalize('NFC') so that visually identical strings written with composed (é, U+00E9) vs decomposed (e + U+0301) forms collapse to a single entry. Order is preserved because the result array is built in iteration order — the Set is consulted only as a 'have I seen this?' filter. The same data structure choice underlies SQL DISTINCT and Python set(); the only real alternative for tens of millions of items is a probabilistic Bloom filter, which trades a small false-positive rate (≈1% at 10 bits/element) for constant memory and is overkill for a browser-side text tool.
- Set lookup uses the SameValueZero algorithm (ECMA-262 §7.2.10) — NaN matches NaN, +0 matches -0, otherwise strict equality
- V8 implements Set as a hash table; insert and has are O(1) amortized, making the whole deduplication O(n) versus indexOf-based O(n²)
- Line mode regex /\r?\n/ handles CRLF, LF, and trailing CR in one split; ignoring this leaves invisible '\r' suffixes that defeat exact matching
- Unicode normalization via String.prototype.normalize('NFC') collapses composed/decomposed forms (e.g. 'é' U+00E9 vs 'e' + U+0301) into one key
- Case-insensitive mode lowercases the key only — the original-case value is preserved in output so the first 'ERROR' is kept verbatim while later 'error' lines are discarded
- Order preservation is free: the result array is built in input order and the Set is consulted only as a filter, so it behaves like SQL DISTINCT with a stable sort
- For 10M+ items where memory becomes the bottleneck, a Bloom filter (≈10 bits/element for 1% false-positive rate) replaces the Set — not needed in-browser, where a Set of 1M strings fits comfortably under 100 MB
Examples
Line deduplication, first occurrence kept
Input:
apple
banana
apple
orange
banana
Output:
apple
banana
orangeLine deduplication with whitespace trimmed
Input:
hello
hello
hello
world
Output (after trim):
hello
worldCase-insensitive deduplication
Input:
ERROR
error
Warning
WARNING
warning
Output (case-insensitive):
ERROR
WarningUnique email list extraction
Input:
alice@example.com
bob@example.com
ALICE@example.com
carol@example.com
bob@example.com
Output (case-insensitive, line mode):
alice@example.com
bob@example.com
carol@example.comWord deduplication
Input: hello world hello again world
Output: hello world againSentence deduplication
Input: This is a test. This is a test. Another sentence.
Output: This is a test. Another sentence.FAQ
What gets considered a duplicate?
Each unit (line, word, sentence, paragraph, or character) is compared against the others. Identical units are duplicates. Toggle case sensitivity on or off. The page outputs the deduplicated list and reports how many duplicates were removed.
Does it preserve order?
Yes - the first occurrence of each unique item is kept in its original position and subsequent duplicates are dropped. The output preserves the original order.
Are blank lines treated as duplicates?
Blank lines are compared like any other line. The first blank line is kept; identical blank lines later in the input are dropped along with other duplicates.
Can it dedupe by a substring or column?
No. Deduplication works on the full content of each unit (line, word, sentence, paragraph, or character). There is no column-based or substring-based deduplication mode.
Will it sort the output?
No. The output always preserves the original order. There is no sort option.
How big a file can it handle?
Browser memory is the limit. Hundreds of thousands of lines work on desktop browsers. Multi-million-line files run out of memory; for those, use a CLI tool like `sort -u` or `awk '!seen[$0]++'`.
Is my text uploaded?
No. Deduplication uses an in-memory Set in your browser. Pasted lines are not transmitted.