title: How to create one box plot using multiple columns and argument "split"
body: <p>I need create a box plot from a data.frame with <strong>three numeric columns</strong>, and use the argument <strong>split</strong> to separate the boxes by <strong>paint</strong>. I have a large data.frame, but what I need is in the example below:</p>
  
  <pre><code>paint&lt;-c("blue", "black", "red", "blue", "black", "red", "blue", "black", "red")
  car1&lt;-c(100, 138, 123, 143, 112, 144, 343, 112, 334)
  car2&lt;-c(111, 238, 323, 541, 328, 363, 411, 238, 313)
  car3&lt;-c(432, 123, 322, 342, 323, 522, 334, 311, 452)
  data&lt;-data.frame(paint, car1, car2, car3)
  
  &gt;data
        paint  car1 car2 car3
     1  blue   100  111  432
     2  black  138  238  123
     3  red    123  323  322
     4  blue   143  541  342
     5  black  112  328  323
     6  red    144  363  522
     7  blue   343  411  334
     8  black  112  238  311
     9  red    334  313  452
  </code></pre>
  
  <p><strong>When I used only one column the following function works:</strong></p>
  
  <p>boxplot(split(data[,2], data[,1]))</p>
  
  <p><strong>But when I try to create a boxplot using <em>three columns</em> the function does not work:</strong></p>
  
  <p>boxplot(split(data[,2:4], data[,1]))</p>
  
  <p>Thanks for the help and sorry for poor English.</p>