Hugo filter a groupby

list.html

{{ define "title" }}People{{ end }}

  {{- range .Pages.GroupByParam "rank_id" }}
    {{/* Need to Substr the Key because we have numerical prefix for sorting */}}
    <h3>{{ substr .Key 2 }}</h3>
    <div class="container">
    {{- range .Pages.ByParam "affiliation" }}
    {{ if eq .Params.current 1 }}
        <div class="col-md-3" style="text-align: center;">
            <div class="caption">
              {{ .Title }}
            </div><!-- end caption -->
        </div><!-- end col --->
    {{ end }}
    {{- end }}
    </div> 
  {{- end }}

{{ end }}