title: LoDash - How to push one collections values into another via common key
body: <p>I have two collections.</p>
  
  <pre><code>var a = 
  [
   {unique_id: "001", state: "CO"},
   {unique_id: "001", state: "TX"},
   {unique_id: "001", state: "CC"},
   {unique_id: "002", state: "CC"},
   {unique_id: "002", state: "NY"}
  ]
  </code></pre>
  
  <p>And</p>
  
  <pre><code>var b = 
  [
   {unique_id: "001", states:[]},
   {unique_id: "002", states:[]}
  ]
  </code></pre>
  
  <p>And I want to get:</p>
  
  <pre><code>var b = 
  [
   {unique_id: "001", states:["CO","TX","CC"]},
   {unique_id: "002", states:["CC","NY"]}
  ]
  </code></pre>
  
  <p>I should mention that the "b" array has to stay in the same order it's in AND some of the unique_id's don't have a value.</p>
  
  <p>I've been trying to use LoDash <a href="https://lodash.com/" rel="nofollow">https://lodash.com/</a> - so if anyone can solve this with LoDash that would be awesome!</p>