# Join the same value elements in single element of array 
use Data::Dumper; 
my @array= (2,2,2,2,3,3,4,4,4,1,1,1); 
my @groups; 
my $group; 
my $i=0; 
my $j=0; 
 
while ($i<$#array) 
{ 
	$group="$array[$i]"; 
	$i++; 
	while ($array[$i]== $array[($i-1)]) 
	{ 
	     $group = join "_ ", $array[$i]; 
		$i++; 
	} 
	push @groups, $group; 
} 
print Dumper @groups;

# For getting original array back 
foreach $elem (@groups) 
{ 
	my @colour_1= split('_ ', $elem); 
       push @colors, @colour_1 ; 
} 
       	print Dumper @colors;

#!/usr/bin/perl  
 
use strict; 
use warnings; 
 
my @array= (2,2,2,2,3,3,4,4,4,1,1,1); 
 
my ($previous, $series, @new_array); 
 
foreach my $current (@array) { 
	unless (defined $previous) { 
		$previous = $current; 
		$series = $current; 
		next; 
	} 
	if ($previous == $current) { 
		$series .= "_" . $current; 
	} 
	else { 
		push @new_array, $series; 
		$series = $current 
	} 
	$previous = $current; 
} 
push @new_array, $series; # adds the last series found 
print "@new_array"; # prints 2_2_2_2 3_3 4_4_4 1_1_1

# For getting original array back  
foreach $elem (@new_array)  
{  
	my @original= split('_ ', $elem);  
       push my @final, @original ;  
}  
       	print "@final"; 
Output: 
2_2_2_2 3_3 4_4_4 1_1_1

my  @new_array= qw/ 2_2_2_2 3_3 4_4_4 1_1_1 /; 
my @resplit =  map {split /_/, $_} @new_array; 
print "@resplit"; # prints "2 2 2 2 3 3 4 4 4 1 1 1"

my  @new_array= qw/ 2_2_2_2 3_3 4_4_4 1_1_1 17_17_17 6_6_6_6_6 8_8/; 
my @resplit =  map {split /_/, $_} @new_array; 
print "@resplit"; 
# prints :  2 2 2 2 3 3 4 4 4 1 1 1 17 17 17 6 6 6 6 6 8 8

input should be  @new_array  and we don't know what is inside.  mean we don't know the string. 
then we do 
my @resplit =  map {split /_/, $_} @new_array;  
print "@resplit";  
 
I want to avoid this  qw/ 2_2_2_2 3_3 4_4_4 1_1_1 17_17_17 6_6_6_6_6 8_8/  

my @array= (2,2,2,2,3,3,4,4,4,1,1,1,2,2,2);