title: PHP push value into sub array of key
body: <p>I have an array of meta that I'm saving for a user that looks like so</p>
  
  <pre><code>$testArray = array("67" =&gt; array("400", "402", "1488"), "84" =&gt; array("599", 620"), "92" =&gt; array("740")
  </code></pre>
  
  <p>If no array for user exists, I need to build it given a key and value</p>
  
  <pre><code>$testArray = ["67" =&gt; ["400"]]
  </code></pre>
  
  <p>If $testArray is not empty, I need to use the key I know to find the corresponding array and add the the value given</p>
  
  <pre><code>$testArray["67"][] = "1500"
  </code></pre>
  
  <p>So the output should be</p>
  
  <pre><code>array("67" =&gt; array("400", "1500"))
  </code></pre>
  
  <p>This method adds nothing to an array that exists and every combination I've tried either adds nothing or a nested array</p>