You've severly misunderstood the use of splice. Did you read the docs?

@a = qw(a b c d );
undef $a[2];

$b{x} = 10 ;
$b{$_} = 1 foreach grep defined, @a;
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or

@a = qw(a b c d );
splice(@a, 2, 1);

$b{x} = 10 ;
$b{$_} = 1 foreach @a;
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