title: How can I resolve the "could not find function vapply" error in R?
body: <p>I installed the stringr package on my Ubuntu 10.04 machine under R 2.10.1. When I try to use the str_extract() function R stops and gives the following error message:</p>
  
  <p>Error in recyclable(string, pattern, replacement) :
     could not find function "vapply"</p>
  
  <p>How can I solve this problem? Is there any specific package that contains this vapply function?</p>