title: Updating Apollo local cache for a specific list/array index
body: <p>I'm using an Apollo local in-memory cache for my app's state management. In my cache I have an array called <code>Clips</code>. Somewhere in my app I need to go through the list of clips and mutate data on them. I can do it like this:</p>
  
  <pre><code>const client = useApolloClient();
  client.writeData({ data: { clips: mutatedClipsArray }});
  </code></pre>
  
  <p>But is there a way that I could write data for only a specific index of the clips array? Something like this (which doesn't work):</p>
  
  <pre><code>client.writeData({ data: { clips[2]: mutatedClip2 }});
  </code></pre>