title: In Twig, check if a specific key of an array exists
body: <p>In PHP we can check if a key exists in an array by using the function <code>array_key_exists()</code>.</p>
  
  <p>In the Twig templating language we can check if an variable or an object's property exists simply by using an <code>if</code> statement, like this:</p>
  
  <pre><code>{% if app.user %}
  do something here
  {% else %}
  do something else
  {% endif %}
  </code></pre>
  
  <p>But how do we check if a key of an <em>array</em> exists using Twig? I tried <code>{% if array.key %}</code>, but it gives me an error:</p>
  
  <pre><code>Key "key" for array with keys "0, 1, 2, 3...648" does not exist
  </code></pre>
  
  <p>As one of the primary ways of passing data into a template is using arrays, it seems like there should be some way of doing this. Any thoughts?</p>