title: Vuejs radio buttons checked if v-model is an array
body: <p>How can i have checked radio button in v-for, if i my v-model is an array?</p>
  
  <p>my data: </p>
  
  <pre><code>data() {
       return {
           persons: {
               name: [],
               surname: [],
               sex: [],
           }
       }
   }  
  </code></pre>
  
  <p>and my radio: </p>
  
  <pre><code>&lt;template v-for(person, person_index) in persons&gt;
  &lt;div class="switch-sex"&gt;
     &lt;input type="radio" name="sex" :id="'male'+person_index" value="male"
     v-model="persons.sex[person_index]"&gt;
     &lt;label :for="'male' + person_index"&gt;M&lt;/label&gt;
     &lt;input type="radio" name="sex" :id="'female' + person_index" 
      value="female" v-model="persons.sex[person_index]"&gt;
     &lt;label :for="'female' + person_index"&gt;F&lt;/label&gt;
  &lt;/div&gt;
  &lt;/template&gt;
  </code></pre>
  
  <p>I need my first radio ( male) be checked in each person inside v-for</p>