title: separating strings by some text within listbox
body: <p>I have a <code>ListBox</code> where table names are written like this:</p>
  <pre><code>Staging_Section_01_2019_03_19_01  
  Staging_Section_01_2019_03_20_01  
  Staging_Section_23_2019_03_21_01  
  Staging_Section_52_2019_03_23_01  
  Staging_Section_52_2019_03_24_01  
  </code></pre>
  <p>What I am trying to do is to separate them by Section Number, so I want all <code>Section_01</code> in one <code>List</code> object and <code>Section_23</code> in another <code>List</code> object, so on and so forth. The dynamic nature is whats making it difficult for me.</p>
  <p>So far, I have the following:</p>
  <pre><code>foreach (var it in uploadBox.Items)
  {
      if (it.ToString().Contains(&quot;Section&quot;))
      {
          section = it.ToString().Substring(0, 18);
          found = it.ToString().IndexOf(&quot;_&quot;);
          section = section.Substring(found + 1);
          sectionNum = section.Substring(8, 2);
      }
  }
  </code></pre>
  <p>I have gotten the <code>sectionNum</code> which would just be the number and section, which is the string like <code>Section_01</code>.</p>
  <p>Any idea on how to approach this?</p>
  <p>The expected output would be something like this:</p>
  <h3>List 1</h3>
  <pre><code>Staging_Section_01_2019_03_19_01  
  Staging_Section_01_2019_03_20_01  
  </code></pre>
  <h3>List 2</h3>
  <pre><code>Staging_Section_23_2019_03_21_01  
  </code></pre>
  <h3>List 3</h3>
  <pre><code>Staging_Section_52_2019_03_23_01  
  Staging_Section_52_2019_03_24_01  
  </code></pre>