title: How to make summary table by group in r?
body: <p>I want make a summary table by group in R<br>
  compare several parameter by factor<br>
  For example </p>
  
  <pre><code>data(iris)
  str(iris)
  </code></pre>
  
  <p>i wanna make table  </p>
  
  <pre><code>     Group   Sepal.Length Sepal.Width Petal.Length Petal.Width
    Species1        mean       mean        mean       mean
    Species2        mean       mean        mean       mean
    Species3        mean       mean        mean       mean 
  </code></pre>
  
  <p>possible import t.test result<br>
  How do i do? </p>