{{ $authors := slice }}
{{ range $index, $data := .Site.Data -}}
  {{- $authors = $authors | append $data.user -}}
{{- end -}}

<author-list>
  <h1>Authors</h1>
  <section>
    {{- range $author := first 3 (shuffle (uniq $authors)) -}}
      {{ $data := index $.Site.Data $author | default "default" }}
      {{ partial "author-card.html" (dict "Data" $data) }}
    {{ end }}
  </section>
</author-list>