title: Composing reducers with nested array
body: <p>I'm using Redux for a while now and I'm loving it :)</p>
  
  <p>I'm a bit confused on how to compose reducers when dealing with nested arrays.  I've a user object, which has a list of reviews. Each review can have a list of review_comments. </p>
  
  <pre><code>{
    user: {
    id: 1, 
    reviews: [{
       id: 1, 
       comments: [{
          id: 1, 
          message: "Test"
       }, {
          id: 2, 
          message: "123"
       }, {
          id: 3, 
          message: "456"
       }]}, {
          id: 2, 
          comments: [{
              id: 5, 
              message: "qwerty"
          }, {
              id: 6, 
              message: "1542354"
          }, {
              id: 7, 
              message: "45we 6"
          }]
      }]
  }}
  </code></pre>
  
  <p>Now, all these are in the same UserReducer. I'm mapping through the list of reviews/ comments every time there is a state change. As the size of my data grows, the reducers become more nested and complex to manage. </p>
  
  <p>Is there a way to compose this into 3 reducers: <code>UserReduce</code>r, <code>ReviewReducer</code> and <code>CommentReducer</code>?</p>
  
  <p>Thanks for the help. </p>