R - Print table with columns sums below
<p>Example: I have a simple data frame </p>

<pre><code>df &lt;- data.frame(date=c("2016-01-01", "2016-01-02")
                 , sales_a = c(2,3)
                 , sales_b = c(1,1)
                 , diff=c(1,2))
</code></pre>

<p>I am currently printing this df using kable in an RMarkDown document. I would like to produce a row underneath with the sums of the columns (not date) with a line separating the df from the totals. Is this possible with any R package without writing latex code which I'm not too familiar with?</p>

<p>Thanks</p>