title: How to insert element into arrays at specific position?
body: <p>Let's imagine that we have two arrays:</p>
  
  <pre><code>$array_1 = array(
    '0' =&gt; 'zero',
    '1' =&gt; 'one',
    '2' =&gt; 'two',
    '3' =&gt; 'three',
  );
  
  $array_2 = array(
    'zero'  =&gt; '0',
    'one'   =&gt; '1',
    'two'   =&gt; '2',
    'three' =&gt; '3',
  );
  </code></pre>
  
  <p>Now, I'd like to insert <code>array('sample_key' =&gt; 'sample_value')</code> after third element of each array. How can I do it?</p>