title: Get first string before separator?
body: <p>I have strings with folowing structure: </p>
  
  <pre><code>7_string_12
  7_string2_122
  7_string3_1223
  </code></pre>
  
  <p>How I can get string before second "_" ?</p>
  
  <p>I want my final result to be :</p>
  
  <pre><code>7_string
  7_string2
  7_string3
  </code></pre>
  
  <p>I am using explode('_', $string) and combine first two values, but my script was very slow!</p>