I assume that the "fields" are the lists in square brackets? If @A = ([0,1],[0,1,2,3,0],[1,2,3,4,1]) then scalar @A is 3 and $#A is 2. Both count the items in the top-level list, and not the number of items in the first field. To count items of a specific field you need to isolate that field, and then use something like scalar grep { BLOCK } @list for counting:

my @A = ([0,1],[0,1,2,3,0],[1,2,3,4,1,1,1,11]);

my $zeroes = scalar grep { $_ == 0 } @{$A[1]};
my $ones =   scalar grep { $_ == 1 } @{$A[2]};

print "Scalar    : ", scalar @A, "\n";
print "Last index: $#A\n";
print "Zeroes in second field: $zeroes\n";
print "Ones   in third  field: $ones\n";
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