title: reshape wide to long in stata but new variable contains all missing values
body: <p>I need to <code>reshape</code> a dataset, whose original form is as follows:</p>
  
  <pre><code>schid     m2s1q0_i     m2s1q0_ii    ...     m2s1q0_x
  1            6            2                   3
  </code></pre>
  
  <p><a href="https://i.stack.imgur.com/3SkW9.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/3SkW9.png" alt="data screenshot"></a>
  I want to <code>reshape</code> it into the long format, like this:</p>
  
  <pre><code>schid teacher_id
  1        5
  1        2
  ...      
  1       3
  </code></pre>
  
  <p>I used this code:</p>
  
  <pre><code>reshape long m2s1q0_, i(schoolid) j(teacher_id)
  </code></pre>
  
  <p>However, the <code>teacher_id</code> variable is all missing. Where did it go wrong?</p>