Oh, wow! I've never heard of PDL. This is spiffy as all get out. Okay, here's how I'd go about it. . .

#here's an array
my @a = (1,2,3);

#now it's a string:
my $string = join '', @a; 

#here's another array

my @b;

#Now the array values your looking for become an array element.
#Increment when those values come up again.
$b[$string]++;

# so $b[123] now = 1

#Leading zeroes disappear, so you could add a 1 to the front of $strin
+g.
$string = '1' . join '', @a;
$b[$string]++;
# so $b[1123] now = 1

#yeah. that'll work

#I might write the whole thing as:
my @a = all your stuff as little array refs from wherever
my @b = the answers you want;
for (@a)
   my $string = '1' . join '', @$_; 
   $b[$string]++
}

#after that, you could copy to an array of tuples:
# e.g., $c[2] = (["123"],[5]); #strip that extra '1' and turn to strin
+g?
#       $c[2] = (["info"], [number of times you find it]);
# might make it easier to play with.

#would %b be faster than @b? I prefer arrays, but that's my bias. 
#$b{$string}++ would certainly work. But, is it as easy to muck about 
+with?
#that extra '1' for referencing the elements does bother me a bit.
[download]