title: Sort WPF datagrid with integer appended with string
body: <p>I have a wpf datagrid. I assign ObservableCollection to it.</p>
  
  <pre><code>DG1.DataContext = a; 
  </code></pre>
  
  <p>One of the columns is having values like following</p>
  
  <pre><code>1_A_B
  12_A1_B
  3_A2_B
  10_A3_B
  2_A4_B
  15_A5_B
  </code></pre>
  
  <p>i want to sort the datagrid using the first integer value like following</p>
  
  <pre><code>1_A_B
  2_A4_B
  3_A2_B
  10_A3_B
  12_A1_B
  15_A5_B
  </code></pre>
  
  <p>If i sort using this column, it is taking as string ascending like following(which is not i want)</p>
  
  <pre><code>1_A_B
  10_A3_B
  12_A1_B
  15_A5_B
  2_A4_B
  3_A2_B
  </code></pre>
  
  <p>I want to sort using the first integer value in above column</p>