title: rowMeans() and mean() return different values?
body: <p>I'm not sure why these two methods for getting the average return different values. The second bit of code is convoluded, I know. This question isn't about making the code better but finding out what the difference is, why they're returning different results.</p>
  
  <p>Thanks!</p>
  
  <pre><code>data(iris)
  sepal_avg &lt;- select(iris, starts_with("Sepal")) %&gt;% rowMeans()
  
  iris$id &lt;- c(1:length(iris$Sepal.Length))
  sepal_avg2 &lt;- iris %&gt;% group_by(id) %&gt;% summarise(sepal_average = mean(Sepal.Length:Sepal.Width))
  
  sepal_avg == sepal_avg2$sepal_average
  </code></pre>