Using the value from a map as a key to another value in the map of a mustache template

Question

I'm using the jknack Java port of Handlebars. I need to create an A-Z list. The key to the map is a letter of the alphabet. At the moment, I have 26 of these in the mustache template:

{{#if A}}<li><a href="#a">A</a></li>{{else}}<li class="unused-letter">A</li>{{/if}}

It would be nice of I could add an array of the letters to the model under the key "keys", for example, and loop through the results:

{{#keys}}
   {{#if .}}<li><a href="#a">{{.}}</a></li>{{else}}<li class="unused-letter">{{.}}</li>{{/if}}
{{/keys}}

However, this doesn't check to see if the map has a key matching the value of the period.

Is there a way of using a value obtained from the map as the key to another object in the map?

Updated information

Looking at Mark's entry I can see that I was approaching the problem from the wrong direction. My model didn't have an entry in the Map if a letter had no results. However, if I update my model so that a key (letter) has an empty list rather than no key/entry at all then I can just use the keys on the Map rather than trying to use another entry to provide values that could represent all possible keys.

Answer 1

I'm not sure what your index data format looks like, so imagine the index was in JSON in this format:

{
   "items":[
      {
         "A":[]
      },
      {
         "B":[
            "dummy",
            "dummy",
            "dummy"
         ]
      },
      {
         "C":[]
      },
      {
         "D":[
            "dummy",
            "dummy",
            "dummy"
         ]
      },
      {
         "E":[]
      },
      {
         "F":[
            "dummy",
            "dummy",
            "dummy"
         ]
      }
   ]
}

Now to iterate through displaying used/unused indexes would require a template like:

<ul>
{{#items}}
{{#each .}}
{{#if .}}
  <li><a href="#{{@key}}">{{@key}}</a></li>
{{else}}
  <li class="unused-letter">{{@key}}</li>
{{/if}}
{{/each}}
{{/items}}
</ul>

which for the above example data would result in:

<ul>
  <li class="unused-letter">A</li>
  <li><a href="#B">B</a></li>
  <li class="unused-letter">C</li>
  <li><a href="#D">D</a></li>
  <li class="unused-letter">E</li>
  <li><a href="#F">F</a></li>
</ul>