# Assume that our input is a list of page/visitor pairs.
# Also, assume that the input is sorted by page.  What we wish
# to do is to print the name of the visited page once, and
# then list all the vistors out on separate lines following
# the page name.

{
  # Do we have a new page yet?
  if ($1 != current_page) { 
    # Yep, new page.  List out all the visitors for the old
    # current_page. 
    print_visitors();
    
    # Reset the list of visitors and continue.
    num_visitors = 0;
    delete visitors;
    printf "%s\n", $1;
    current_page = $1;
  }
}

{ 
  # Record this visit.
  visitors[num_visitors] = $2
  num_visitors++;
}

END {
  # Be sure to list the visitors for the last page, too.
  print_visitors();
}

function print_visitors () {
  # We want to print each visitor only once.
  for (v in visitors) {
    if (!printed[visitors[v]]) {
      printf "\t\t%s\n", visitors[v];
      printed[visitors[v]] = 1;
    }
  }
  delete printed
}