title: Get percentage with ddply function
body: <p>I want to divide the percent into Korea and Taiwan separately.
  I don't have any idea to calculate the percent with <code>ddply</code> fucntion separately.</p>
  
  <pre><code>plot&lt;-ddply(
      data, 
      c("Country", "Here.is.usually.much.garbage.distributed."),
      summarise,
      n=length(Here.is.usually.much.garbage.distributed.),
      percent=((n/sum(plot$n))*100)
  )
  
  </code></pre>
  
  <p>Is there anyone who knows how to do it?</p>
  
  <blockquote>
    <p>plot
      <a href="https://i.stack.imgur.com/0DLnL.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/0DLnL.png" alt="enter image description here"></a></p>
  </blockquote>