I have a loop that goes through a folder of markdown files and displays the titles of each in a dropdown. I need to be able to filter the results of the loop based on whether or not a markdown file has an "office" value in it.

I currently have this:

```
<select name="practice-area" type="search" class="practice-areas-list select-table-filter" data-table="order-table">
    <option value="default">Practice Areas</option>
    {% for practice_area in site.practice_areas %}
      {% unless practice_area.office %}
        <option value="{{ practice_area.title }}">{{ practice_area.title }}</option>
      {% endunless %}
    {% endfor %}
  <select>

```

where `{% unless practice_area.office %}` should be checking if the file has `office` in it. If so, pull title into list.

**Sample Markdown File**

```
---
title: page title
slug: page-title
office: 
-22
---

```

Not sure of the proper Jekyll syntax for this to work correctly.