title: Increment counter in nested v-for
body: <p>I have a nested data structure like so:</p>
  
  <pre><code>allItems: [
      ['a', 'b', 'c'],
      ['d', 'e', 'f'],
      ['g', 'h', 'i'],
  ]
  </code></pre>
  
  <p>that I need to represent exactly like this:</p>
  
  <pre><code>Category 1
  ..........(a) Item 1
  ..........(b) Item 2
  ..........(c) Item 3
  Category 2
  ..........(d) Item 4
  ..........(e) Item 5
  ..........(f) Item 6
  Category 3
  ..........(g) Item 7
  ..........(h) Item 8
  ..........(i) Item 9
  </code></pre>
  
  <p>But I am not able to keep a counter in between v-for...
  Note that I have no control over the data and user will be offered to sort data however he wants making it impossible for me to add a counter within the data.</p>
  
  <p>Here is a <a href="https://jsfiddle.net/4je123th/2/" rel="noreferrer">fiddle</a></p>