How to render custom data in Bootstrap-Vue Table component?

I am using Bootstrap-Vue and VueJs and need help with some custom data rendering from multiple data objects and displaying the data into a table. Specifically, I am following this part of the Bootstrap-Vue TABLE docs: https://bootstrap-vue.js.org/docs/components/table#formatter-callback but I am unsure how to apply it to my code.

Here's my scenario:

I have a data API providing 2 different arrays of objects: posts and names

Posts:

    [
  {
    "userId": 1,
    "id": 1,
    "title": "sunt aut facere repellat provident occaecati excepturi optio reprehenderit",
    "body": "quia et suscipit\nsuscipit recusandae consequuntur expedita et cum\nreprehenderit molestiae ut ut quas totam\nnostrum rerum est autem sunt rem eveniet architecto"
  },
...snip..
    ]

and Names:

[{"userId":1,"first_name":"Neill","last_name":"Dexter","email":"[email protected]"},
...snip
]

The posts array contains a userId key but no name of the user. The names array contains the userId key and the first_name and last_name of that user.

What I want to do is simply display the full name of the user in my Bootstrap-vue Table component rather than the userId because just showing the userId doesn't make sense.

Here's my attempt (link to editable live code):

<template>
  <div>
    <b-table :items="posts" :fields="fields">
      <!-- A custom formatted column -->
      <template slot="name" slot-scope="data">{{ data.value.userId }}</template>
    </b-table>
  </div>
</template>

<script>
import axios from "axios";
export default {
  data() {
    return {
      posts: [],
      names: [],
      // key name is the slot name
      fields: [
        { key: "id" },
        { key: "title" },
        { key: "body" },
        { key: "name", label: "Assigned To", formatter: "assignNames" }
      ]
    };
  },
  created() {
    this.getPosts();
    this.getNames();
  },
  methods: {
    getPosts() {
      axios.get("https://jsonplaceholder.typicode.com/posts").then(resp => {
        this.posts = resp.data;
      });
    },
    getNames() {
      axios
        .get("https://my.api.mockaroo.com/users.json?key=f119e0f0")
        .then(resp => {
          this.names = resp.data;
        });
    },
    assignNames() {
      var i;
      for (i = 0; i < this.posts.length; i++) {
        if (this.posts[i].userId !== null) {
          const result = this.names.filter(name => {
            return name.userId === this.posts[i].userId;
          });
          this.posts[i].userId =
            result[0].first_name + " " + result[0].last_name;
        }
      }
    }
  }
};
</script>

Anyone got any tips on how I can show the full name of my users rather than just the userId? Thanks!