Since titles are so finicky, a more common method of linking book entities (if available) is to use bibliographic codes like ISBNs. Unfortunately for us (but, I suppose, fortunate from a pedagogical point of view), a quick look at our ISBNs reveals there's nonsense going on there, too, as you can see in the following code:
> lib$ISBN[1] "9781447286813" "147460725X" "144205374-7 "[4] "9780525433576" "1-405-88229-8" "8496886611fsds34Recur"[7] NA "889882002x" "978-0060000578"
Some of the problems that we can spot are:
- ISBN-13s are mixed with ISBN-10s
- Some of the check digits (the last character of an ISBN) are x and some are upper case
- Some of the ISBNs are hyphenated and some are not
- One of the ISBNs have trailing whitespace ...
