gcg-website/layouts/partials/filter-controls.html

<ul class="list-inline text-center filter-controls mb-4">
  {{ $categories := slice }}
  {{ if ne (len .Data.Pages) 0 }}
    {{ range .Data.Pages }}
      {{ $categories = $categories | append .Params.category }}
    {{ end }}
  {{ else }}
    {{ range .Params.tiles }}
      {{ with .category }}
        {{ $categories = $categories | append . }}
      {{ end }}
    {{ end }}
  {{ end }}
  {{ if ne (len $categories) 0 }}
    <li class="list-inline-item m-3 text-uppercase active" data-filter="all">Alle</li>
  {{ end }}
  {{ range ( $categories | uniq ) }}
    <li class="list-inline-item m-3 text-uppercase" data-filter="{{ . | urlize }}">{{ . | humanize }}</li>
  {{ end }}
</ul>