title: Number of significant digits in dplyr summarise
body: <p>I am having trouble getting the desired number of decimal places from summarise. Here is a simple example:</p>
  
  <pre><code>test2  &lt;- data.frame(c("a","a","b","b"), c(245,246,247,248))
  library(dplyr)
  colnames(test2)  &lt;- c("V1","V2")
  group_by(test2,V1) %&gt;% summarise(mean(V2))
  </code></pre>
  
  <p>The dataframe is:</p>
  
  <pre><code>  V1  V2
  1  a 245
  2  a 246
  3  b 247
  4  b 248
  </code></pre>
  
  <p>The output is:</p>
  
  <pre><code> V1     `mean(V2)`
   &lt;fctr&gt;      &lt;dbl&gt;
  1 a             246
  2 b             248
  </code></pre>
  
  <p>I would like it to give me the means including the decimal place (i.e. 245.5 and 247.5)</p>