JSFiddle - React, Tailwind, and code Playground

HTML

<div class="item"><a href=""><img src="" class="group1"></a></div>
<div class="item"><a href=""><img src="" class="group1"></a></div>
<div class="item"><a href=""><img src="" class="group2"></a></div>
<div class="item"><a href=""><img src="" class="group2"></a></div>
<div class="item"><a href=""><img src="" class="group3"></a></div>
<div class="item"><a href=""><img src="" class="group3"></a></div>
<div class="item"><a href=""><img src="" class="group3"></a></div>

JavaScript

var classes = {};
$(".item img").each(function(){
    var className = $(this).attr('class');
    classes[className] = true;
});
for(var elem in classes){
    $(".item img." + elem).closest(".item")
    .wrapAll('<div class="' + elem +'"></div>');   
}