title: How to apply the wilcox.test to a whole dataframe in R?
body: <p>I have a data frame with one grouping factor (the first column) with multiple levels (more than two) and several columns with data. I want to apply the <em>wilcox.test</em> to the whole date frame to compare the each group variables with the others. How can I do this?</p>
  
  <p>UPDATE:
  I know that the <em>wilcox.test</em> will only test for difference between two groups and my data frame contains three. But I am interested more in how to do this, than what test to use. Most likely that one group will be removed, but I have not decided yet on that, so I want to test all variants.</p>
  
  <p>Here is a sample:</p>
  
  <pre><code>structure(list(group = c(1L, 1L, 1L, 1L, 1L, 1L, 2L, 2L, 2L, 
  2L, 2L, 2L, 2L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L), var1 = c(9.3, 
  9.05, 7.78, 7.11, 7.14, 8.12, 7.5, 7.84, 7.8, 7.52, 8.84, 6.98, 
  6.1, 6.89, 6.5, 7.5, 7.8, 5.5, 6.61, 7.65, 7.68), var2 = c(11L, 
  11L, 10L, 1L, 3L, 7L, 11L, 11L, 11L, 11L, 4L, 1L, 1L, 1L, 2L, 
  2L, 1L, 4L, 8L, 8L, 1L), var3 = c(7L, 11L, 3L, 7L, 11L, 2L, 11L, 
  5L, 11L, 11L, 5L, 11L, 11L, 2L, 9L, 9L, 3L, 8L, 11L, 11L, 2L), 
      var4 = c(11L, 11L, 11L, 11L, 6L, 11L, 11L, 11L, 10L, 7L, 
      11L, 2L, 11L, 3L, 11L, 11L, 6L, 11L, 1L, 11L, 11L), var5 = c(11L, 
      1L, 2L, 2L, 11L, 11L, 1L, 10L, 2L, 11L, 1L, 3L, 11L, 11L, 
      8L, 8L, 11L, 11L, 11L, 2L, 9L)), .Names = c("group", "var1", 
  "var2", "var3", "var4", "var5"), class = "data.frame", row.names = c(NA, 
  -21L))
  </code></pre>
  
  <p><strong>UPDATE</strong></p>
  
  <p>Thanks to everyone for all answers!</p>