I don't know whether this helps, but your array names seem to show an "off by one" issue in your way of thinking. Change the array names to encourage correct thoughts...

my @RowZero = ("a","b","c");
my @RowOne = ("d","e");
my @RowTwo = ("f","g","h","i");
my @TwoDimArray = (\@RowZero,\@RowOne,\@RowTwo);
my $ChosenRow = 1;

my @chosen_array = @{$TwoDimArray[$ChosenRow]};
my $num_chosen_items = @chosen_array;

print "I chose row $ChosenRow (counting from 0),\n".
      " containing $num_chosen_items things: @chosen_array\n";
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Works for me, as far as it goes.