You could even tweak your resulting array a bit to accumulate counts of instances of the bigram rather than just saving '1' or '0':

use strict;
use warnings;

my @bg_data
    = qw( aa aa aa sd gd sd bf bf sd gd sd df sb eb xd bf dr et bf bf 
+sd bd
          aa aa aa ab ab ab ab ab ab ab ab ab sb eb ad ad ad ad ad bf 
+sd bd );

# Note and accumulate how many times each bigram is used....
my %bg_stats;
$bg_stats{$_}++ foreach @bg_data;
    
# Store the data in the 676-element array....
my @bg_final = map{ $bg_stats{$_} ||= 0 } ( 'aa' .. 'zz' );

#print "$_\n" foreach @bg_final;
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