bash_n_examples/perl/shuffle

   1 #!/usr/bin/env perl
   2 #
   3 # Print input data in random order.
   4 #
   5 # TODO FYS algorithm works on in-memory array; way to shuffle while
   6 # streaming over the input, similar to "print random line from file?"
   7 # (shuf, apparently, if you have that toolset)
   8
   9 my @input = readline;
  10
  11 die "error: no data supplied to shuffle\n" unless @input;
  12
  13 fisher_yates_shuffle( \@input );
  14
  15 print for @input;
  16
  17 # fisher_yates_shuffle( \@array ) : generate a random permutation
  18 # of @array in place
  19 sub fisher_yates_shuffle {
  20     my $array = shift;
  21     my $i;
  22     for ( $i = @$array; --$i; ) {
  23         my $j = int rand( $i + 1 );
  24         next if $i == $j;
  25         @$array[ $i, $j ] = @$array[ $j, $i ];
  26     }
  27 }
  28
  29 END {
  30     # Report problems when writing to stdout (perldoc perlopentut)
  31     unless ( close(STDOUT) ) {
  32         warn "error: problem closing STDOUT: $!\n";
  33         exit 74;
  34     }
  35 }