Re: Cutting the top percentage out of a Hash

[johngg]

It is probably a good idea to take the plunge and try new modules as other Monks have suggested. However, I have put a script together to show you one way of preserving your insertion order when using hashes. I have used hash references, sometimes called anonymous hashes, which are useful when building complex data structures. Doing $refToHash = {} creates a reference to an empty hash. They are also useful for passing data into and out of subroutines.

I have taken a random subset of the X11 rgb.txt file as data source in order to build a hash of colours. They are in no particular order but the order they are in can be preserved. I have also used Data::Dumper so you can see what the data structure looks like after we have constructed it.

use strict;
use warnings;

# Use this to show the data structure.
#
use Data::Dumper;

# Initialise a hash reference and a sequence no.
#
my $rhPreserve = {};
my $insertionOrder = 0;

# Read our data line by line, chomping off the newline
# and splitting on the ":" and using the colour name
# as the key and RGB for the value.
#
while(<DATA>)
{
    chomp;
    my ($value, $key) = split /:/;

    # Make an entry in the hash reference for this colour but
    # the value is another hash with two key/value pairs, one
    # for our RGB value and the other the insertion order
    # which we increment after insertion.
    #
    $rhPreserve->{$key} =
    {
       value => $value,
       insertionOrder => $insertionOrder ++
    };
}

# Use Data::Dumper to print out the hash reference so we can see
# what we have constructed. The colour "keys" will come out in an
# order determined by the underlying hashing algorith.
#
my $dd = Data::Dumper->new([$rhPreserve], ["rhPreserve"]);
print "Data structure\n", $dd->Dumpxs();

# To use our insertion order, which we have preserved in the hash
# reference, we can sort by "insertionOrder" then use the sorted keys
# to access the hash reference.
#
my @keysInInsertionOrder =
   sort
   {
      $rhPreserve->{$a}->{insertionOrder}
      <=>
      $rhPreserve->{$b}->{insertionOrder}
   }
   keys %$rhPreserve;
print "Data in insertion order\n";
foreach (@keysInInsertionOrder)
{
    print
       "Insertion order - $rhPreserve->{$_}->{insertionOrder}\n",
       "     Key - $_\n",
       "     Value - $rhPreserve->{$_}->{value}\n";
}

__END__
255 250 250:snow
248 248 255:GhostWhite
245 245 245:WhiteSmoke
220 220 220:gainsboro
255 250 240:FloralWhite
253 245 230:OldLace
250 240 230:linen
250 235 215:AntiqueWhite
255 239 213:PapayaWhip
255 235 205:BlanchedAlmond
255 228 196:bisque
255 218 185:PeachPuff
255 222 173:NavajoWhite
255 228 181:moccasin
255 248 220:cornsilk
255 255 240:ivory
255 250 205:LemonChiffon
255 245 238:seashell
240 255 240:honeydew

When run this produces the following

Data structure
$rhPreserve = {
                'LemonChiffon' => {
                                    'value' => '255 250 205',
                                    'insertionOrder' => 16
                                  },
                'cornsilk' => {
                                'value' => '255 248 220',
                                'insertionOrder' => 14
                              },
                'bisque' => {
                              'value' => '255 228 196',
                              'insertionOrder' => 10
                            },
                'GhostWhite' => {
                                  'value' => '248 248 255',
                                  'insertionOrder' => 1
                                },
                'WhiteSmoke' => {
                                  'value' => '245 245 245',
                                  'insertionOrder' => 2
                                },
                'PapayaWhip' => {
                                  'value' => '255 239 213',
                                  'insertionOrder' => 8
                                },
                'honeydew' => {
                                'value' => '240 255 240',
                                'insertionOrder' => 18
                              },
                'NavajoWhite' => {
                                   'value' => '255 222 173',
                                   'insertionOrder' => 12
                                 },
                'OldLace' => {
                               'value' => '253 245 230',
                               'insertionOrder' => 5
                             },
                'AntiqueWhite' => {
                                    'value' => '250 235 215',
                                    'insertionOrder' => 7
                                  },
                'linen' => {
                             'value' => '250 240 230',
                             'insertionOrder' => 6
                           },
                'ivory' => {
                             'value' => '255 255 240',
                             'insertionOrder' => 15
                           },
                'PeachPuff' => {
                                 'value' => '255 218 185',
                                 'insertionOrder' => 11
                               },
                'snow' => {
                            'value' => '255 250 250',
                            'insertionOrder' => 0
                          },
                'seashell' => {
                                'value' => '255 245 238',
                                'insertionOrder' => 17
                              },
                'FloralWhite' => {
                                   'value' => '255 250 240',
                                   'insertionOrder' => 4
                                 },
                'moccasin' => {
                                'value' => '255 228 181',
                                'insertionOrder' => 13
                              },
                'gainsboro' => {
                                 'value' => '220 220 220',
                                 'insertionOrder' => 3
                               },
                'BlanchedAlmond' => {
                                      'value' => '255 235 205',
                                      'insertionOrder' => 9
                                    }
              };
Data in insertion order
Insertion order - 0
     Key - snow
     Value - 255 250 250
Insertion order - 1
     Key - GhostWhite
     Value - 248 248 255
Insertion order - 2
     Key - WhiteSmoke
     Value - 245 245 245
Insertion order - 3
     Key - gainsboro
     Value - 220 220 220
Insertion order - 4
     Key - FloralWhite
     Value - 255 250 240
Insertion order - 5
     Key - OldLace
     Value - 253 245 230
Insertion order - 6
     Key - linen
     Value - 250 240 230
Insertion order - 7
     Key - AntiqueWhite
     Value - 250 235 215
Insertion order - 8
     Key - PapayaWhip
     Value - 255 239 213
Insertion order - 9
     Key - BlanchedAlmond
     Value - 255 235 205
Insertion order - 10
     Key - bisque
     Value - 255 228 196
Insertion order - 11
     Key - PeachPuff
     Value - 255 218 185
Insertion order - 12
     Key - NavajoWhite
     Value - 255 222 173
Insertion order - 13
     Key - moccasin
     Value - 255 228 181
Insertion order - 14
     Key - cornsilk
     Value - 255 248 220
Insertion order - 15
     Key - ivory
     Value - 255 255 240
Insertion order - 16
     Key - LemonChiffon
     Value - 255 250 205
Insertion order - 17
     Key - seashell
     Value - 255 245 238
Insertion order - 18
     Key - honeydew
     Value - 240 255 240

I hope this will help.

Cheers,

JohnGG