title: How to calculate combination and permutation in R?
body: <p>How one can calculate the number of combinations and permutations in R?</p>
  <p>The <a href="http://rss.acs.unt.edu/Rdoc/library/Combinations/html/00Index.html" rel="noreferrer">Combinations package</a> failed to install on Linux with the following message:</p>
  <pre><code>&gt; install.packages(&quot;Combinations&quot;)
  Installing package(s) into ‘/home/maxim/R/x86_64-pc-linux-gnu-library/2.13’
  (as ‘lib’ is unspecified)
  Warning message:
  In getDependencies(pkgs, dependencies, available, lib) :
    package ‘Combinations’ is not available (for R version 2.13.1)
  </code></pre>