title: smoothing line with categorical variable with ggplot?
body: <p>I have a huge data sets and this is a sample.</p>
  
  <pre><code>data.frame(basket_size_group = c("[0,2]", "[0,2]", "(2,4]", "(2,4]", "(4,6]"),
         channel = c("offline", "online/mobile", "offline", "online/mobile", "offline"), 
         pct_trips = c(0.004, 0.038, 0.0028, 0.0082, 0.0037))
  </code></pre>
  
  <p>By using a <code>ggplot2</code>, I would like to plot smoothing line with the data. Xaxis is the <code>basket_size_group</code>, yaxis is <code>pct_trips</code>, <code>channel</code> is a group in <code>ggplot2</code> . The problem is that <code>basket_size_group</code> is a categorical variable. How to create smoothing lines by <code>channel</code> with <code>ggplot2</code>?</p>