v-for accordion index
<div class="panel-group" id="accordion" role="tablist" aria-multiselectable="false">
<ul>
<li v-for="(item, index) in items" :key="index">
<div class="panel panel-default">
<div class="panel-heading" role="tab" id="headingOne">
<h4 class="panel-title">
{{ item.name }}
<div align="right">
<btn role="button" data-toggle="collapse" data-parent="#accordion" aria-expanded="false" :data-target="'#collapse-' + index" aria-controls="'#collapse-' + index">Select</btn>
</div>
</h4>
</div>
<div :id="'collapse-' + index" class="panel-collapse collapse" role="tabpanel" aria-labelledby="headingOne">
<div class="panel-body">
Drop down {{ index }}.
</div>
</div>
</div>
</li>
</ul>
</div>