JSFiddle - React, Tailwind, and code Playground

HTML

<ul>
    <li data-cat="one">test
    <li data-cat="one">test
    <li data-cat="two">test
    <li data-cat="three">test
    <li data-cat="three">test
    <li data-cat="three">test
</ul>

CSS

.active {
    color: red;
}

JavaScript

var cats = {};
var list = $( '[data-cat]' ).filter(function(){
    var category = $(this).data("cat");
    
    if(cats[category]){
        return false;   
    } else {
        cats[category] = true;
        return true;
    }
}).addClass('active');