title: The most efficient way to reorder columns in SAS
body: <p>I have a data <code>temp</code> that contains variables A1, A2, ... Amax. I want to rearrange its internal order so that once we open it, it will show A2, A5, .....</p>
  
  <p>I know there's couple of ways to do this. What I usually to is to use <code>retain</code> statement. </p>
  
  <p>If the number of observation is large (N>1,000,000), what's the most efficient way to finish this? A data step with <code>retain</code> or <code>proc sql</code> or something else? </p>
  
  <p>The most efficient means the least processing time for me. I will appreciate if you can also provide the analysis of the memory and disk space needed for each method.</p>