merge columns of two dataframes : <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>
