title: merge columns of two dataframes
body: <p>How can two dataframes be quickly merged? 
  dataframes</p>
  
  <pre><code>df1&lt;-data.frame(a=(1:5),b=(1:5))
  df2&lt;-data.frame(c=(1:5),d=(1:5))
  </code></pre>
  
  <p>intended output:</p>
  
  <pre><code>output&lt;-data.frame(a=(1:5),b=(1:5),c=(1:5),d=(1:5))
  </code></pre>