Like previous posters have said use splice(@arr, $off, $len) to delete items from your lists, though if you can't use slice then you will have to test for definedness yourself. Example:

my @a = qw( a b c d );
# delete a & c
splice(@a, 0, 1)
splice(@1, 1, 1)
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As for converting the array into a hash while preserving the previous contents something like this will do the job nicely:

my @a = qw( a b c d );
my %b = ( 'e' => 2 );
%b = (%b, map { $_ => 1} grep defined, @a);
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This preserves the previous contents of %b while adding keys for @a into %b.