title: Angular 4 - .filter is not a function
body: <p>I have this code:</p>
  
  <pre><code> transform(searchData: Array&lt;vw_WebSiteCourseSearch&gt;, searchResultContentType: string) {
          if (searchData == undefined) {
              return;
          }
  
          return searchData.filter((item) =&gt; item.ContentType == searchResultContentType);
      }
  </code></pre>
  
  <p>My console prints:</p>
  
  <pre><code>ERROR TypeError: searchData.filter is not a function
  at FilterCountPipe.webpackJsonp.../../../../../src/app/Common/pipes/filterCount.pipe.ts.FilterCountPipe.transform (filterCount.pipe.ts:19)
  </code></pre>
  
  <p>I tried to add import from rxjs/add/operator/filter, but it didn't solved it.
  Any ideas on how to fix it?</p>
  
  <p>Thanks</p>