uniqWith()

uniqWith(str, comparator): string

Creates a duplicate-free version of a string using a custom comparator.

💎 Why is this a Hidden Gem?

No native equivalent for character-level deduplication with custom logic. Useful for case-insensitive or locale-aware uniqueness.

note

Keeps first occurrence of each character. O(n²) complexity.

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Parameters

str: string

The string to process.

comparator: (a, b) => boolean

Function to compare characters for equality.

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Returns: string

The string with unique characters (first occurrence kept).

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Since

2.0.0

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Performance

O(n²) time, O(n) space where n is string length. Uses every() for each character check.

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Also known as

dedupeWith (Effect) · uniqWith (Lodash, es-toolkit, Remeda, Ramda) · unique (Radashi) · ❌ (Modern Dash, Antfu)

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Example

uniqWith('hello', (a, b) => a === b);
// => 'helo'

uniqWith('Hello', (a, b) => a.toLowerCase() === b.toLowerCase());
// => 'Helo'

uniqWith('hello   world', (a, b) => /\s/.test(a) && /\s/.test(b));
// => 'hello world'

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How it works?

Creates a duplicate-free version of a string using a custom comparator.

Example: Case-insensitive

Comparator Examples

Comparator	Input	Output
(a, b) => a === b	'hello'	'helo'
(a, b) => a.toLowerCase() === b.toLowerCase()	'Hello'	'Helo'
(a, b) => /\s/.test(a) && /\s/.test(b)	'a b c'	'a b c'

Performance

O(n²) time complexity due to every() check for each character.

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Use Cases

Filter unique characters 📌

Remove duplicate characters based on custom logic (e.g., case-insensitive). Useful for generating unique sets of symbols or cleaning input.

#filter#unique#characters#deduplication#case-insensitive#custom

const unique = uniqWith('aAaB', (a, b) => a.toLowerCase() === b.toLowerCase());
// 'aB'

Remove consecutive duplicates

Filter out repeated characters while preserving first occurrence.

#remove#consecutive#duplicates#repeated#cleaning#filtering

const clean = uniqWith('aaabbbccc', (a, b) => a === b);
// 'abc'