title: Regex replace on specific column with SED/AWK
body: <p>I have data that looks like this (TAB delimited):</p>
  
  <pre><code>Organ K     ClustNo Analysis
  LN    K200  C12     Gene Ontology
  LN    K200  C116    Gene Ontology
  CN    K200  C2      Gene Ontology
  </code></pre>
  
  <p>What I want to do is to remove <code>C</code> for every row on <em>3rd column</em>, except header row:</p>
  
  <pre><code>Organ K     ClustNo Analysis
  LN    K200  12      Gene Ontology
  LN    K200  116     Gene Ontology
  CN    K200  2       Gene Ontology
  </code></pre>
  
  <p>This won't do because it will affect other columns and header row:</p>
  
  <pre><code>sed 's/C//'
  </code></pre>
  
  <p>What's the right way to do it?</p>