title: Filter IEnumerable
body: <p>I have 3 classes with the following properties:</p>
  
  <p>OfferList class:</p>
  
  <pre><code>Guid Id
  IEnumerable&lt;Offer&gt; Offers
  </code></pre>
  
  <p>Offer class:</p>
  
  <pre><code>Guid Id
  Product Product
  bool IsSealed
  </code></pre>
  
  <p>Product class:</p>
  
  <pre><code>Guid Id
  </code></pre>
  
  <p>An OfferList contains multiple Offers and an Offer has exact 1 Product.</p>
  
  <p>How can I filter the OfferList to contain only Offers which are not sealed?</p>
  
  <pre><code>OfferList offerList = this.GetOfferList(id).Offers.Where(o =&gt; !o.IsSealed));
  </code></pre>
  
  <p>This returns an IEnumerable of type Offer instead of filtering the OfferList.</p>