how to use v-for index as value for href - vue.js

Question

I am using VueJS along with foundation css. I am trying to create an accordion from a v-for loop. However VueJS wants me to bind the href to the projectIndex variable.
I have tried creating a projectIndex parameter and then using a computed property to return a concatenation of "#" + projectIndex, but projectIndex is always undefined.
data: {
projectIndex: ''
}
....
computed:{
projectHref: function () {
return "#" + this.projectIndex;
}
}
Out of interest I am using [[]] rather than {{}} because I am also using twig which shares the same {{}} as VueJS
<ul class="accordion" data-accordion>
<li class="accordion-navigation" v-for="(priceData, projectIndex) in prices">
Price Project: [[priceData.meta.project.name]]
<div id="[[projectHref]]">
<div v-for="(prices, supplier) in priceData.prices">
<h6>[[supplier|SupplierKeyName]] ([[supplier|SupplierKeyCode]])</h6>
<table class="table">
<tr>
<td v-for="(price, priceBreak) in prices">[[priceBreak]]</td>
</tr>
<tr>
<td v-for="(price, priceBreak) in prices">[[price.currency]][[price.price]]</td>
</tr>
</table>
</div>
</div>
</li>
</ul>

Answer 1

is the prices variable already set?
if yes, then I think it is replaced by your second v-for that use same prices variable, so that the for loop breaks away
//here is the first 'prices' variable
<li class="accordion-navigation" v-for="(priceData, projectIndex) in prices">
Price Project: [[priceData.meta.project.name]]
<div id="[[projectHref]]">
//here the prices variable is replaced
<div v-for="(prices, supplier) in priceData.prices">
try to differentiate those vars

Answer 2

OK, I found the solution. I found that I could bind to a method and pass projectIndex in as a value. like so
<li class="accordion-navigation" v-for="(priceData, projectIndex) in prices">
<a :href="projectHref(projectIndex)">Price Project: [[priceData.meta.project.name]]</a>
My method then returns the concatonation that I needed.
methods: {
projectHref: function (index) {
return "#" + index.toString();
}
}