<ul class="list-inline text-center filter-controls mb-4">
  <li class="list-inline-item m-3 text-uppercase active" data-filter="all">Alle</li>
  {{ $categories := slice }}
  {{ range .Data.Pages }}
    {{ $categories = $categories | append .Params.category }}
  {{ end }}
  {{ range ( $categories | uniq ) }}
    <li class="list-inline-item m-3 text-uppercase" data-filter="{{ . | urlize }}">{{ . | humanize }}</li>
  {{ end }}
</ul>