Jekyll output collection list organized by tag -

i'm having trouble grouping items tags in collection. i've managed site.categories (check bellow), i'm having trouble fecthing yaml attributes collection items in same way.

{% imagens in site.imagens %}  <div class="card">   <ul class="lista-imagens">    <li><a class="categories" name="{{ imagens.tags | first }}">{ {{     imagens.tags | first }} }</a>   <ul >    <li>     <img src="{{ imagens.image_path }}" alt="{{ imagens.title }}">     <a href="{{ imagens.original_path }}" target="_blank">{{ imagens.title }}</a>     <span class="ano">{{ imagens.year }}</span>     </li>       </ul>   </li>  </ul> </div> {% endfor %}   {% category in site.categories %} <div class="col-md-3">  <ul class="listinha"> <li><a class="categories" name="{{ category | first }}">{ {{ category | first }} }</a>   <ul >   {% posts in category %}     {% post in posts %}       <li><a href="{{ post.url }}">{{ post.title }}</a>  <br>       <span class="autor"> {{ post.author }} {% if post.year %}<br> {{ post.year }} {% endif %} </span><span class="contributor">{{ post.contributor }} <!-- / imgs: {{ post.imgs }}<br>--></span></li>     {% endfor %}   {% endfor %}   </ul>  </li> </ul> </div> {% endfor %}