title: How to merge two columns in R with a specific symbol?
body: <p>I have a table read in R as follows:</p>
  
  <pre><code>column1 column2
  A        B
  </code></pre>
  
  <p>What is the command to be used to match two columns together as follows?</p>
  
  <pre><code>Column 3
  A_B
  </code></pre>