If I've understood want you want, $TwoDimArray[$ChosenRow] will get you an arrayref of the chosen row. To get an array from the reference, dereference it using @{ ... }. ie

my @ChosenArray = @{ $TwoDimArray[$ChosenRow] };
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To find the number of elements, assign @{ $TwoDimArray[$ChosenRow] } in scalar context:

my $elements = @{ $TwoDimArray[$ChosenRow] };
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