title: Count array key that contain specific string
body: <p>I have an array like that contain key with same name but with number at the end</p>
  
  <p>array example:</p>
  
  <pre><code>Array
  (
      [field_name0] =&gt; name 
      [field_name1] =&gt; sku_package_height 
      [field_name2] =&gt; sku_package_width
      [custom_field] =&gt; 13
      [attribute] =&gt; 'test'
      [field_name3] =&gt; sku_package_length 
      [field_name4] =&gt; sku_package_weight
  )
  </code></pre>
  
  <p>from the example above i want to count how many record that has array key that contain <code>field_name</code>, so the result I want will be <code>5</code></p>