vuejs set a radio button checked if statement is true

Maybe someone finds this approach helpful:

In template I assign each radio button a value:

<input type="radio" value="1" v-model.number="someProperty">
<input type="radio" value="2" v-model.number="someProperty">

Then in the component I set the value, i.e:

data: function () {
    return {
        someProperty: 2
    }
}

And in this case vue will select the second radio button.

You could bind the checked attribute like this:

<div v-for="portal in portals">
  <input type="radio"
         id="{{portal.id}}"
         name="portalSelect"
         v-bind:value="{id: portal.id, name: portal.name}"
         v-model="newPortalSelect"
         v-on:change="showSellers"
         :checked="portal.id == currentPortalId">

  <label for="{{portal.id}}">{{portal.name}}</label>
</div>

Simple example: https://jsfiddle.net/b4k6tpj9/