title: What does `.Z` mean in SAS?
body: <p>Apologies for such an entirely uninformed question, but I don't know any SAS and just need to know what one line of code does, so I hope someone can help. 
  I have a loop over an array of variables, and an if clause that is based on a comparison to <code>.Z</code>, but this variable is defined nowhere, so I'm guessing this is some sort of SAS syntax trick. Here's the loop:</p>
  
  <pre><code>ARRAY PTYPE{*} X4216 X4316 X4416 X4816 X4916 X5016;
  
  DO I=1 TO DIM(PTYPE);
      IF (PTYPE{I}&lt;=.Z) THEN PUT &amp;ID= PTYPE{I}=;
  END;
  </code></pre>
  
  <p>So on the first iteration, the loop would check whether the value in <code>X4216</code> is smaller than <code>.Z</code>, and then...? <code>ID</code> is another varuable in the dataset, but I have no idea what's happening on the right hand side of that if clause. I've briefly consulted the SAS documentation to figure out that ampersands refer to macros, but my knowledge of SAS is to limited to understand what's happening.</p>
  
  <p>Can anyone enlighten me?</p>