title: Merging columns on alphabetic order
body: <p>I have 4 columns that I want to merge.</p>
  
  <pre><code>CHR POS EFFECT_ALLELE NON_EFFECT_ALLELE
  1   124 A             C           
  5   378 C             T  
  3   398 T             C  
  3   564 G             A  
  </code></pre>
  
  <p>I want them to be merged in the following way:
  <code>CHR:POS:EFFECT_ALLELE:NON_EFFECT_ALLELE</code></p>
  
  <p>However, I want "EFFECT_ALLELE:NON_EFFECT_ALLELE" to be merged on alphabetical order. </p>
  
  <p>So for the lines above it would be:  </p>
  
  <pre><code>1:124:A:C  
  5:378:C:T  
  3:398:C:T  
  3:564:A:G  
  </code></pre>
  
  <p>So, for the third and fourth example above it has to be "NON_EFFECT_ALLELE:EFFECT_ALLELE'</p>
  
  <p>Can anyone help me with the coding of merging "NON_EFFECT_ALLELE" and "EFFECT_ALLELE" on alphabetical order?</p>
  
  <p>Thanks in advance!</p>