Re: How to bucket a Hash

[Athanasius]

Hello techman2006,

Your question implies that the code shown works correctly. But what happens if you have an odd number of elements in the hash? Running your code with %hash = ( 1 => 'a', 2 => 'b', 3 => 'c', 4 => 'd', 5 => 'e' ) I get:

16:51 >perl 786_SoPW.pl
Total keys are 5
$VAR1 = {
          '1' => 'a',
          '5' => 'e'
        };
$VAR1 = {
          '4' => 'd',
          '3' => 'c'
        };
$VAR1 = [
          {
            '1' => 'a',
            '5' => 'e'
          },
          {
            '4' => 'd',
            '3' => 'c'
          }
        ];

16:51 >

which shows that the fifth element is left out altogether.

Anyway, here is my solution, a variation on hdb’s approach which uses the natatime function from List::MoreUtils:

#! perl
use strict;
use warnings;
use Data::Dump      qw( pp );
use List::MoreUtils qw( natatime );

my  $i    = 1;
my  %hash = map { $i++ => $_ } 'a' .. 'e';
print 'Initial hash: ', pp(\%hash), "\n";

my $it = natatime 2, sort { $a <=> $b } keys %hash;
my @array_of_hashes;

while (my @keys = $it->())
{
    my %new_hash = map { ( $_, $hash{$_} ) } @keys;
    push @array_of_hashes, \%new_hash;
}

print 'Array of hashes: ', pp(\@array_of_hashes), "\n";

Update: Changed 'a' .. 'j' to 'a' .. 'e', and the first argument to natatime from 4 to 2, to match the output shown.

Output:

16:54 >perl 786_SoPW.pl
Initial hash: { 1 => "a", 2 => "b", 3 => "c", 4 => "d", 5 => "e" }
Array of hashes: [{ 1 => "a", 2 => "b" }, { 3 => "c", 4 => "d" }, { 5 
+=> "e" }]

16:55 >

Hope that helps,

[techman2006]

That was a test program and it didn't take care of the all the cases :). Thanks for fixing that issue.

As I was looking to different solutions which can be used while assigning jobs to multiple threads. As I want a fixed size queue is assigned to each thread. As the job items are present in a HASH, I was looking a method through which this slicing can be done on a faster way as the total keys can be high.

[Random_Walk]

Why do you want a fixed work unit size for each thread? Given the vagaries of multitasking, some thread is sure to finish a fixed length task before another doing the same size task. Why not just pour all your data into a Thread::Queue and have a pool of workers servicing this queue? If you have a very large amount of data it can also be handy to have a size limited queue, BrowserUK gives a great example here: Re^5: dynamic number of threads based on CPU utilization.

Cheers,
R.