@{ $hoa{ $k } } = [ $val1[ $idx ], $val2[ $idx ] ];
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I think you'd either want to remove the @{} notation, or else change your square brackets to parentheses. Your line there is creating a strange data structure there :)

# this
@{ $hoa{ $k } } = ( $val1[ $idx ], $val2[ $idx ] );

# or this
$hoa{ $k } = [ $val1[ $idx ], $val2[ $idx ] ];
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