IEnumerable<type> does not contain a definition of 'Contains'
<p>I have 2 classes and 2 IEnumerable lists of those classes:</p>
<pre><code>public class Values
{
    public int Value { get; set; }
    public DateTime SomeDate { get; set; }
}

public class Holidays
{
    public DateTime holiday { get; set; }
}

IEnumerable&lt;Values&gt; values;
IEnumerable&lt;Holidays&gt; holidays;
</code></pre>
<p>Next, I am trying to select those 'values' where 'someDate' is not in 'holidays'</p>
<pre><code>var query = values.Where(x=&gt; !holidays.Contains(x.someDate));
</code></pre>
<p>However, this gives me the error of <code>IEnumerable&lt;Holidays&gt; does not contain a definition of 'Contains'</code>.</p>
<p>System.Linq is already added in the <code>using</code>s.</p>
<p>I believe this has to do something with the collections, but am not able to figure what.</p>