title: Calculate percentages across columns
body: <p>So I have a data.frame in R studio I've made with the following columns</p>
  
  <pre><code>Site               sumofspecies1       sumofspecies2      totalspecies
  uniquesite         500                 1000               1500
  uniquesite2        1000                500                1500
  </code></pre>
  
  <p>I'd like to make a data frame that changes these values to be</p>
  
  <pre><code>Site               sumofspecies1       sumofspecies2      totalspecies
  uniquesite         33.3%               66.6%              1500
  uniquesite2        66.6%               33.3%              1500
  </code></pre>
  
  <p>Or something to that effect it seems easy enough however I'm having a lot of difficulty finding a similar case online or in the documentation</p>
  
  <p>Cheers</p>