title: Merge array without loss key index
body: <p>i have two array</p>
  
  <pre><code>/**
   * Menu Navigation
   * @var array
   */
  public $nav_top = array(
      100 =&gt; 'Dashboard',
      200 =&gt; 'Sell',
      300 =&gt; 'Products',
      400 =&gt; 'History',
      500 =&gt; 'Customers',
      600 =&gt; 'Setup'
  );
  
  /**
   * Menu Navigation
   * @var array
   */
  public $nav_sub = array(
      201 =&gt; 'Current Sale',
      202 =&gt; 'Retrieve Sale',
      203 =&gt; 'Close Register',
  
      301 =&gt; 'Product',
      302 =&gt; 'Stock Control',
      303 =&gt; 'Price Books',
      304 =&gt; 'Types',
      305 =&gt; 'Suppliers',
      306 =&gt; 'Brands',
      307 =&gt; 'Tags',
  
      501 =&gt; 'Customer',
      502 =&gt; 'Group'
  );
  </code></pre>
  
  <p>How to combine this two array without losing it's key index?</p>
  
  <p>if i do it with <code>array_merge()</code> the index will restart from zero</p>
  
  <pre><code>$nav = array_merge($Class-&gt;nav_top, $Class-&gt;nav_sub);
  var_dump($nav);
  
  # Output:
  array(
      0 =&gt; 'Current Sale',
      1 =&gt; 'Retrieve Sale',
      2 =&gt; 'Close Register',
      .......
  );
  </code></pre>
  
  <p>expected result the array key still same</p>
  
  <pre><code># Expected Output
  array(
      100 =&gt; 'Dashboard',
      200 =&gt; 'Sell',
      300 =&gt; 'Products',
      ........
  );
  </code></pre>