I couldn’t find a histogram library for Perl, so I had to write my own.

Save the following code in histogram.pl:

   1  use POSIX qw(ceil floor);
   2  
   3  # No bugs, please
   4  use strict;
   5  use warnings;
   6  
   7  # Perl doesn't have round, so let's implement it
   8  sub round
   9  {
  10      my($number) = shift;
  11      return int($number + .5 * ($number <=> 0));
  12  }
  13  
  14  sub histogram
  15  {
  16    my ($bin_width, @list) = @_;
  17  
  18    # This calculates the frequencies for all available bins in the data set
  19    my %histogram;
  20    $histogram{ceil(($_ + 1) / $bin_width) -1}++ for @list;
  21  
  22    my $max;
  23    my $min;
  24  
  25    # Calculate min and max
  26    while ( my ($key, $value) = each(%histogram) )
  27    {
  28      $max = $key if !defined($min) || $key > $max;
  29      $min = $key if !defined($min) || $key < $min;
  30    }
  31  
  32  
  33    for (my $i = $min; $i <= $max; $i++)
  34    {
  35      my $bin       = sprintf("% 10d", ($i) * $bin_width);
  36      my $frequency = $histogram{$i} || 0;
  37  
  38      $frequency = "#" x $frequency;
  39  
  40      print $bin." ".$frequency."\n";
  41    }
  42  
  43    print "===============================\n\n";
  44    print "    Width: ".$bin_width."\n";
  45    print "    Range: ".$min."-".$max."\n\n";
  46  }

To generate a histogram for a set of data include the histogram subroutine and pass the desired width of the bins to the routine and the dataset as an array:

   1  do('histogram.pl');
   2  
   3  histogram(10, (1,2,3,4,5,10,11,12,20,21,30));

The output of the above example is:

   1  0  #####
   2  10 ###
   3  20 ##
   4  30 #
   5  
   6  ===============================
   7  
   8  Width: 10
   9  Range: 0-3

The generated histogram tells us that there are: 5 numbers between 0-9, 3 between 10-19, 2 between 20-29, 1 between 30-39